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Full text of "Poly(amide-graft-acrylate) interfacial compounds"



POLY ( AMI DE-GRAFT-ACRYLATE) INTERFACIAL COMPOUNDS 



By 
MICHAEL PEREZ ZAMORA 



A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL 

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT 

OF THE REQUIREMENTS FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

UNIVERSITY OF FLORIDA 

1997 



This dissertation is dedicated to all those who supported me 

emotionally, physically, and financially throughout my 

seemingly endless years of education; especially my wife 

Karen, my parents Pablo and Sylvia, and my grandmother 

Bella; and to the loving memory of Oscar Zamora and Manuel 

Leon . 



ACKNOWLEDGMENTS 

I cannot express enough gratitude and appreciation to 
my advisor and doctoral committee chairman, Dr. Anthony 
Brennan, for his years of teaching, guidance and support in 
areas that extended well beyond my academic endeavors. I 
would also like to express sincere thanks to the members of 
my supervisory committee for their advice and teaching: Dr. 
Jim Adair, Dr. Chris Batich, Dr. Eugene Goldberg, and Dr. 
Ken Wagener. 

I consider this experience substantially enriched by 
the support of my colleagues. Whether there was 
collaboration, debate or simply encouragement, it would have 
been endlessly more difficult without the following: Dr. 
Michael Antonell, Dr. Drew Amery, Craig Habeger, Jeff 
Kerchner, Dr. James Marotta, Jeremy Mehlem, Dr. Rodrigo 
Orefice, Luxsamee Plangsmangas, Mark Schwarz, and Dr. Chris 
Widenhouse . 

Special thanks are extended to Arthur Gavrin for his 
assistance with NMR spectroscopy and for the lively 
discussions in his short time here, and Ananth Naman and Dr. 
Rob Chodelka for their unwavering support and friendship. I 
would be remiss not to mention Jesse Arnold and Tom Miller, 
my colleagues of five years with whom I have grown, matured, 

iii 



and learned. I will forever be appreciative of our 
continuous discussions, debates, and collaboration as well 
as their undying support. 



:i v 



TABLE OF CONTENTS 

ACKNOWLEDGMENTS iii 

LIST OF TABLES viii 

LIST OF FIGURES ix 

ABSTRACT xiii 

1 . INTRODUCTION 1 

1.1. Poly (amide-g-acrylate) Graft Copolymers 1 

1.1.1. Macromonomers 1 

1.1.2. Addition-Condensation Graft Copolymers 3 

1.1.3. Applications 4 

1.2. Offsetting Polymerization Shrinkage in Dental 
Resins through the Incorporation of Maleic 
Anhydride 5 

2 . BACKGROUND 7 

2.1. Graft Copolymers 8 

2.1.1. Synthetic Routes to Graft Copolymers 8 

2.1.1.1. Anionically polymerized macromonomers 9 

2.1.1.2. Macromonomers through chain transfer 

f unctionalization 9 

2.1.1.3. Modeling chain transfer reaction 15 

2.1.2. Polyamide Addition-Condensation Multiphase 
Copolymers 19 

2.1.2.1. Poly (amide-b-olef in) block copolymers.... 19 

2.1.2.2. Poly (amide-g-olef in) graft copolymers.... 28 

2.2. Polymerization Shrinkage in Dental Composites 35 

2.2.1. History of Dental Composites 36 

2.2.2. Reduction of Polymerization Shrinkage in 
Dental Resins 39 

2.2.3. Use of Anhydrides in Dental Applications 41 

2.2.4. Filler Modification in the Reduction of 
Overall Composite Shrinkage 42 

3 . MATERIALS AND METHODS 4 4 

3.1. Materials 44 

3.1.1. Macromonomer Reactants 44 

3.1.2. Graft Copolymer Reactants 45 

3.1.3. Dental Monomers 45 

3.2. Methods 46 



3.2.1. Synthesis and Characterization of 
Macromonomers 4 6 

3.2.2. Synthesis and Characterization of Graft 
Copolymers 4 9 

3.2.3. Synthesis and Characterization of Anhydride 
Modified Dental Resins 52 

RESULTS AND DISCUSSION 55 

4.1. Synthesis and Characterization of Amino Acid- 
terminated Poly (acrylate) Macromonomers using 

Chain Transfer Chemistry 55 

4.1.1. Determination of an Appropriate Solvent 

System 59 

4.1.2. Preliminary Studies of the Effectiveness of 
Cysteine as a Chain Transfer Agent in the 
Polymerization of Butyl Acrylate 61 

4.1.3. Determination of Chain Transfer Constant of 
Cysteine in the Synthesis of Amino Acid- 
terminated Poly (butyl acrylate) Macromonomers 75 

4.1.4. Cysteine Chain Transfer in the Synthesis of 
Amino Acid-terminated Poly (methyl 
methacrylate : octaf luoropentyl methacrylate) 
Macromonomers 8 8 

4.2. Polyamide-g-poly (acrylate) graft copolymers 

from Amino Acid-terminated Macromonomers 99 

4.2.1. Synthesis of Poly (amide-g-butyl acrylate) .... 99 

4.2.2. Characterization of Graft Copolymers 104 

4.2.3. Blends of Graft Copolymers with Nylon 6 139 

4.3. Offsetting Polymerization Shrinkage in Dental 
Resins through the Incorporation of Maleic 
Anhydride 144 

4.3.1. Copolymer Compositions 146 

4.3.2. Copolymer Characterization 149 

SUMMARY AND CONCLUSIONS 158 

5.1. Chain Transfer Functionalization of 

Poly (acrylates) and Poly (methacrylates) 161 

5.1.1. Conclusions for Preliminary Evaluation of 

Cysteine Chain Transfer Agent 161 

5.1.2 Conclusions for Synthesis and 
Characterization of Amino Acid-terminated 

Poly (butyl acrylate) 162 

5.1.3 Conclusions for Synthesis and 
Characterization of Amino Acid-terminated 

Poly (MMA-co-OFPMA) 162 

5.2. Graft Copolymerizations of Macromonomers with 

Polyamide Precursors 163 

5.2.1. Conclusions for Synthesis of Poly (amide-g- 

acrylate) Graft Copolymers 164 



VI 



5.2.2. Conclusions for Characterization of 

Poly (amide-g-acrylate) Graft Copolymers 165 

5.2.3. Conclusions for Mechanical Properties of 

Nylon 6/Graf t Copolymer Blends 166 

5.3. Offsetting Polymerization Shrinkage in 

Poly (dimethacrylate) Dental Resins 166 

5.3.1. Conclusions for Characterization of Maleic 
Anhydride-containing Dental Resins 167 

5.3.2. Conclusions for Synthesis and 
Characterization of Anhydride Copolymer with 

PEMA 168 

6. FUTURE WORK 169 

6.1. Macromonomers and Graft Copolymers 169 

6.1.1. Macromonomer Work 169 

6.1.2. Graft Copolymers 170 

6.2. Anhydride-containing Dental Resins 171 

LIST OF REFERENCES 173 

BIOGRAPHICAL SKETCH 181 



Vll 



LIST OF TABLES 
TABLE page 

4.1 Solvent determination for monomer and chain 

transfer agent °0 

4.2 Percent f unctionalization versus molar mass for 

poly (butyl acrylate) macromonomers 87 

4.3 Molar mass values of f luoroacrylate copolymers from 
GPC 91 

4.4 Percent weight loss from Soxhlet extraction for 
polyamide graft copolymers 105 

4.5 Chemical composition of purified graft copolymers from 
elemental analysis and NMR 137 

4.6 Inherent viscosities of polyamide graft copolymers. 138 

4.7 Tensile properties of nylon 6 blends 140 

4.8 Experimental matrix of dental monomer compositions. 148 

4.9 PEMA-maleic anhydride monomer compositions 14 9 

4.10 EWC of maleic anhydride dental resins 150 

4.11 Residual weight gain, anhydride incorporation and post 
polymerization expansion of maleic anhydride dental 
resins 151 

4.12 Glass transition temperatures and composition of PEMA- 
maleic anhydride copolymers 155 

4.13 Molar mass averages from GPC for PEMA-anhydride 
copolymers 157 



LIST OF FIGURES 
Figure page 

1.1 Schematic illustration of general graft copolymer 
structure 1 

2.1. Mechanism of f unctionalization using chain transfer 
agents 11 

2.2. Schematic illustration of utilized chain transfer 
agents and macromonomers thereof 16 

2.3. Mechanism of block copolymer formation through 
sequential polymerizations of vinyl monomer and 
isocyanates 21 

2.4. Reaction schematic for macroinitiator formation and 
subsequent anionic block polymerization of caprolactam. 

23 

2.5 Reaction schematic of block copolymerization initiated 
by nitrosated polyamide macroinitiators 25 

2 . 6 Reaction schematic of AIBN containing polyamide and 
block copolymer thereof 27 

2.7 Reaction schematic of in situ graft copolymer formation 
from glycidyl methacrylate copolymers 31 

2.8 Reaction schematic of in situ graft copolymer formation 
from maleic anhydride modified polyolefins copolymers.. 

33 

2.9 Mechanism of ring opening polymerization of spiro 
orthocarbonate monomers 40 

4.1. Mechanism of functionalization using chain transfer 

reactions 57 

4.2 Schematic of ideal amino acid functionalization during 
polymerization of butyl acrylate 62 



1 X 



4.3 GPC results of preliminary butyl acrylate 

polymerizations 64 

4 . 4 DSC trace of side product 66 

4.5 FTIR spectra of side product of cysteine modified 

P (BA) 67 

4.6 Comparison of FTIR spectra of side product with butyl 
acrylate monomer 68 

4.7 Reaction pathway of cysteine with acrylates 69 

4.8 Structure and elemental analysis of side product. ... 70 

4.9 Side reaction preventing complete chain transfer. ... 73 

4.10 Effect of acidification on chain transfer 
functionalization of poly (butyl acrylate) 76 

4.11 GPC results of polymerizations of butyl acrylate 
varying cysteine concentrations 80 

4.12 Mayo plot for chain transfer constant determination for 
cysteine rbutyl acrylate system 81 

4.13 FTIR spectra of poly (butyl acrylate) and cysteine end- 
capped p(BA) macromonomer . Macromonomer is the 

1.2 kg/mo 1 p(BA) synthesized using 1000:64:1 butyl 
acrylate : cysteine :AIBN mole ratio 83 

4.14 1 H-NMR spectra of neat poly (butyl acrylate) 84 

4.15 H-NMR spectra of 1.2 kg/mo 1 cysteine modified 
poly(butyl acrylate) 85 

4.16 13 C-NMR spectra of 1.2kg/mol cysteine modified 

poly (butyl acrylate) 86 

4.17 Chemical structure of f luoroacrylate copolymer 90 

4.18 GPC result of chain transfer polymerizations of 

f luoroacrylate copolymers 91 

4.19 Comparison of effectiveness of chain transfer for p(BA) 
and f luoroacrylate copolymer 93 

4.20 x H-NMR spectra of MMA-OFPMA macromonomer 95 



4.21 Mayo plot for chain transfer constant determination for 
cysteine :MMA-co-OFPMA system 96 

4.22 FTIR spectra of MMA-OFPMA copolymers 98 

4.23 Amide-acrylate graft copolymer structure 100 

4.24 Triphenyl phosphite driven amide formation 102 

4.25 Synthesized graft copolymer compositions 103 

4.26 Molar mass distributions of dissolved polymer in THF 
extractant solution of 33PABA-g-66BA (refractive index 
detector) 107 

4.27 UV spectra of dissolved polymer in THF extractant 
solution of 33PABA-g-66BA from GPC-UV 108 

4.28 Molar mass distributions of dissolved polymer in THF 
extractant solution of 33PhDAA-g-66BA (refractive index 
detector) 110 

4.29 UV spectra of dissolved polymer in THF extractant 
solution of 33PhDAA-g-66BA from GPC-UV 112 

4.30 Molar mass distributions of dissolved polymer 
in THF extractant solution of 10PhDAA-g-90BA 
(refractive index detector) 113 

4.31 UV spectra of dissolved polymer in THF extractant 
solution of 10PhDAA-g-90BA from GPC-UV 114 

4.32 Molar mass distributions of dissolved polymer in THF 
extractant solution of 33PhDAA-g-66FA (refractive index 
detector) 116 

4.33 UV spectra of dissolved polymer in THF extractant 
solution of 33PhDAA-g-66FA from GPC-UV 117 

4.34 Molar mass distributions of dissolved polymer in THF 
extractant solution of 33PhDAA-g-66UBA (refractive 
index detector) 119 

4.35 UV spectra of dissolved polymer in THF extractant 
solution of 33PhDAA-g-66UBA from GPC-UV 120 

4.36 Transmission FTIR spectra of 66PABA-g-33BAx graft 
copolymer 122 

4.37 Transmission FTIR spectra of 33PABA-g-66BAx graft 
copolymer 123 



XI 



4.38 Transmission FTIR spectra of 33PhDAA-g-66BAx graft 
copolymer 125 

4.39 Transmission FTIR spectra of 10PhDAA-g-90BAx graft 
copolymer 126 

4.40 Transmission FTIR spectra of poly (butyl acrylate) 
grafted polyamides 128 

4.41 Transmission FTIR spectra of 10PhDAA-g-90BAx graft 
copolymer 129 

4.42 ^-NMR spectra of 66PABA-g-33BAx 131 

4.43 ^-NMR spectra of 33PABA-g-66BAx 132 

4.44 ^-NMR spectra of PhDAA homopolyamide 133 

4.45 X H-NMR spectra of 33PhDAA-g-66BAx 134 

4.46 ^-NMR spectra of 10PhDAA-g-90BAx 135 

4.47 ^-NMR spectra of 33PhDAA-g-66FAx 136 

4.48 TG/DTA analysis of 33PhDAA-g-66BA graft copolymer and 
PhDAA homopolyamide 142 

4.49 DSC analysis of 33PhDAA-g-66BA graft copolymer and 
PhDAA homopolyamide 143 

4.50 Chemical structures of methacrylate and anhydride 
monomers for dental applications 147 

4.51 TG/DTA of anhydride modified dental resin 153 

4.52 FTIR spectra of poly(PEMA) and poly ( 60PEMA-co-40maleic 
anhydride) 154 



Xll 



Abstract of Dissertation Presented to the Graduate School 

of the University of Florida in Partial Fulfillment of the 

Requirements for the Degree of Doctor of Philosophy 



POLY(AMIDE-GRAFT-ACRYLATE) INTERFACIAL COMPOUNDS 

By 

Michael Perez Zamora 

December, 1997 

Chairman: Dr. Anthony B. Brennan 

Major Department: Materials Science and Engineering 

Graft copolymers with segments of dissimilar 
chemistries have been shown to be useful in a variety of 
applications as surfactants, compatibilizers, impact 
modifiers, and surface modifiers. The most common route to 
well defined graft copolymers is through the use of 
macromonomers, polymers containing a reactive functionality 
and thus capable of further polymerization. However, the 
majority of the studies thus far have focused on the 
synthesis of macromonomers capable of reacting with vinyl 
monomers to form graft copolymers . 

This study focused on the synthesis of macromonomers 
capable of participating in condensation polymerizations. A 
chain transfer f unctionalization method was utilized. 
Cysteine was evaluated as a chain transfer agent for the 
synthesis of amino acid f unctionalized poly (acrylate) and 
poly (methacrylate) macromonomers. Low molar mass, 
functionalized macromonomers were produced. These 
macromonomers were proven to be capable of reacting with 



amide precursors to form poly (amide-g-acrylate) graft 
copolymers . 

Macromonomers and graft copolymers were characterized 
by gel permeation chromatography (GPC) , Fourier transform 
infrared spectroscopy (FTIR), nuclear magnetic resonance 
(NMR) spectroscopy, elemental analysis (EA) , inductively 
coupled plasma (ICP), and differential scanning calorimetry 
(DSC) . 

The second part of this research involved 
poly (dimethacrylate) dental restorative materials. 
Volumetric shrinkage during the cure of these resins results 
in a poor interface between the resin and the remaining 
tooth structure, limiting the lifetime of these materials. 
Cyclic anhydrides were incorporated into common monomer 
compositions used in dental applications. Volume expansion 
from the ring opening hydrolysis of these anhydrides was 
shown to be feasible. 

The modified dental resins were characterized by 
swelling, extraction and ultraviolet spectroscopy (UV) , and 
density measurements. Linear polymers designed to model the 
crosslinked dental resins were characterized by FTIR, GPC, 
and DSC. 



CHAPTER 1 
INTRODUCTION 



1.1. Poly (amide-g-acrylate) Graft Copolymers 

Graft copolymers are macromolecules composed of 
chemically dissimilar segments in a branched architecture 
(Figure 1.1) . They have been studied and utilized in a 
variety of applications because of their ability to combine 
the properties of their individual segments. 




Figure 1.1 Schematic illustration of general graft 
copolymer structure. 



1.1.1 .Macromonomers 



The most prevalent synthetic route to well defined 
graft copolymers is through the use of macromonomers, low 



molar mass polymers containing a polymerizable end group. A 
review of the literature has shown that current studies, 
including those within this laboratory, have concentrated on 
synthesizing macromonomers which contain a residual 
unsaturation at one end. Therefore, they are generally 
polymerizable only with addition type monomers through a 
free radical mechanism. Because the macromonomers 
themselves are generally synthesized through either anionic 
or free radical polymerization in the presence of a 
f unctionalizing agent, the resulting graft copolymers which 
can be synthesized through this method are generally limited 
to addition-addition graft copolymers . 

It was the objective of the first part of this study to 
synthesize condensation polymerizable macromonomers, 
specifically amino acid terminated macromonomers, capable of 
reacting with amino acids in the synthesis of polyamide 
graft copolymers. An amino acid functionality is preferred 
over other end groups such as diacids or diamines due to the 
inherent stoichiometry that it provides. This stoichiometry 
is required in the condensation graft reaction to insure the 
highest degree of polymerization possible. 

The approach taken in this study involves the free 
radical polymerization of acrylate and methacrylate monomers 
in the presence of a functional chain transfer agent. 
Mercaptans, compounds containing a sulfur-hydrogen bond, are 
commonly used in chain transfer reactions. In fact, 
mercaptans are commonly used to control molecular weight in 



commercial polymerization reactors. Cysteine, a naturally 
occurring amino acid, contains the sulfhydryl group required 
for mercaptan chain transfer reactions. The addition of 
cysteine, if effective as a chain transfer agent, would 
result in an amino acid functionality. 

1 . 1 . 2 .Addition-Condensation Graft Copolymers 

There are few reports of well defined polyamide graft 
copolymers with addition polymers such as poly (acrylates ) or 
poly (methacrylates) . Most studies of amide graft 
copolymerizations with addition polymers involve either the 
in situ formation of graft copolymers in polymer blends or 
radiation induced surface graft techniques. Although 
effective for their intended applications, neither method 
produces a well defined graft copolymer that can be isolated 
and studied. 

The objective of the second part of this research was 
to evaluate the ability of the previously synthesized 
macromonomers to participate in a condensation 
polymerization of polyamide precursors. If successful, the 
resulting structure would be a poly (amide-g-acrylate) graft 
copolymer . 

The properties of the synthesized macromonomers and 
graft copolymers were characterized by a variety of 
techniques including GPC, FTIR spectroscopy, NMR 



spectroscopy, UV spectroscopy, elemental analysis, ICP, and 
DSC. 

1.1.3 .Applications 

One of the most common applications of graft copolymers 
is their use as compatibilizers . The appropriate graft 
copolymer has been shown to migrate to the interface between 
two dissimilar materials, reducing interfacial tension and 
increasing the bonding at the interface. 

The initial motivation for the study of polyamide- 
polyacrylate graft copolymers came from the field of 
dentistry. The new class of dental restorative composites, 
better known as 'fillings' consist of a crosslinked 
dimethacrylate matrix surrounding glass particles. The 
failure of dental restorative composites, and poor 
performance as compared to amalgam restorations, is 
generally attributed to a poor interface. Although the 
glass-resin interface has been studied extensively, the 
source of failure is usually the interface between the 
composite restoration and the remaining tooth structure. 

Two of the main sources of this poor interface are 

1) poor bonding between the exposed tooth structure, 
composed of hydrophilic proteinaceous dentin tubules 
and the hydrophobic dimethacrylate composite and 

2) the polymerization shrinkage during composite cure 
causing the restoration to pull away from the remaining 



tooth structure. This leads to marginal leakage, the 
infiltration of saliva and bacteria under the 
restoration, which can lead to the secondary caries. 
The macromonomer and graft copolymer work was targeted to 
determine the ability to synthesize a copolymer capable of 
interacting with both the hydrophobic methacrylate and 
hydrophilic dentin structure at the tooth-restoration 
interface. Although the synthesized amide-acrylate graft 
copolymers were not tested in such a system and their 
aromatic structures may not make them suitable for this 
application, the feasibility of synthesizing the desired 
structures has been evaluated. 



1.2. Offsetting Polymerization Shrinkage in Dental Resins 
through the Incorporation of Maleic Anhydride 



The last part of this research addresses the 
polymerization shrinkage problem in these dental resins. 
This shrinkage is inherent to the free radical 
polymerization of the multifunctional methacrylate resins 
used in the dental composites. The volumetric shrinkage is 
due to the reduction in molar volume, or spacing between 
monomer units, that occurs when vinyl compounds are 
polymerized. Polymerization shrinkage creates both a weak 
interface between the tooth structure and the restoration as 
well as residual stresses within the composite structure, 
leading to premature failure in the restoration. 



There are many research programs focused on different 
chemical structures and processes that will reduce 
polymerization shrinkage. Although various methods and 
different monomers have been studied to alleviate this 
problem, no solution to date has been discovered that 
eliminates shrinkage without significantly altering the cure 
and mechanical properties of the resin. 

The goal of this study was to demonstrate that we can 
offset the polymerization shrinkage of common dimethacrylate 
resins without significantly changing the comonomer 
structures through the copolymerization with maleic 
anhydride. When maleic anhydride (MA) is ring opened by 
hydrolysis to maleic acid, there is a corresponding 
theoretical 10% increase in molar volume. 

The properties of the anhydride-methacrylate 
copolymers, including the ability of the anhydride to offset 
the polymerization shrinkage, were characterized by 
swelling, extraction and ultraviolet spectroscopy (UV) , and 
density measurements, FTIR, GPC, and DSC. 



CHAPTER 2 
BACKGROUND 



The first section of this chapter addresses how our 
study of amino acid-terminated poly (acrylate) macromonomers 
and poly (amide-g-acrylate) graft copolymers fits within the 
massive amount of literature on the synthesis and 
characterization of multiphase copolymers. An overview of 
graft copolymers is given, followed by a description of the 
methodology and limitations of common synthetic routes as 
they relate to synthesizing addition-condensation graft 
copolymers. This is followed by an analysis of other 
studies concentrating specifically on polyamide graft and 
block copolymers. 

As was mentioned previously, the initial motivation for 
amide-acrylate graft copolymers comes from the field of 
dental materials. Specifically, the failure of dental 
restorative materials at the tooth-resin interface is of 
concern. It was mentioned that one of the main causes of 
this failure is the cure shrinkage of these resins during 
application, causing the resin to pull away from the tooth 
surface. The second part of this chapter addresses the 
problem of polymerization shrinkage in dental resins, and 



analyzes the approaches described in the literature to 
alleviate this problem. 

2.1. Graft Copolymers 

Graft and block multiphase copolymers have received an 
increasing amount of attention over the past twenty years. 
They have been shown to possess desirable combinations of 
physical and chemical properties that allow them to be 
useful in a variety of applications (Nos77, Pei86, Nat88, 
Tan90, Zha90, Pei94) including blend compatibilizers, 
surfactants, impact modifiers, and surface modifiers. 

All of the applications mentioned take advantage of the 
individual properties of chemically dissimilar segments. 
Most of these depend on the ability of these copolymers to 
act at a particular interface. For example, these 
copolymers can be added to a blend of two immiscible 
homopolymers that have affinities for the individual 
segments of the multiphase copolymer. The copolymer 
migrates to the interface between the two phases (Shu90) , 
reducing the interfacial tension (Gai80, Ana89) and thus 
enhancing the strength of the interface (Fay82, Bro89, 
Cre89) . 

2 . 1 . 1 . Synthetic Routes to Graft Copolymers 

One of the most widely used methods of synthesizing 
multiphase copolymers is through sequential anionic block 



copolymerization (Has83) . But the number of monomers that 
can be polymerized anionically is limited due to unwanted 
side reactions (Has83) . The stringent polymerization 
conditions required for the anionic polymerization of 
certain monomers (Nos77) also limits its applicability. 
These limitations severely reduce the applicability of this 
route to a wide variety of combinations of block segments. 
In order to expand the possible combinations of monomers 
used as the two phases, graft copolymerizations have been 
investigated (Mei73) . 
2 . 1 . 1 . 1 .Anionically polymerized macromonomers 

One of the most prevalent and reliable synthetic routes 
to graft copolymers is through the use of macromonomers 

(Cor84, Rem84b, Muh87, Mei90, Pei94). Macromonomers are end 
functional macromolecules capable of further polymerization 

(Rem84a) . They are generally synthesized through the 

anionic polymerization of a monomer followed by reaction of 

the living anion with an end capping agent such as 

methacryloyl chloride, producing a methacrylate or vinyl 

terminated macromonomer (Mas82, Sch82, Ham84, Sch84a, 

Sch84b, Cam85, Cam86, Gna87, Gna88) . Once again, 

application of this synthetic procedure is limited in scope 

due to monomer restrictions in anionic polymerizations. 

2 . 1 . 1 . 2 .Macromonomers through chain transfer 
functionalization 

A more versatile route to macromonomers involves the 

free radical polymerization of a monomer in the presence of 



10 



a functional chain transfer agent (Ito77). Functionalized 
mercaptans are commonly used. Mercaptans are compounds 
containing a sulfhydryl, -SH, functional group. They are 
commonly used to control molecular weight in commercial 
polymerization reactors (Ros82). 

The mechanism by which f unctionalization can occur is 
depicted in Figure 2.1. Steps 1 and 2 are typical process 
of free radical initiation. When exposed to heat, the AIBN 
breaks down into free radicals and nitrogen gas is evolved. 
The AIBN radicals can thus initiate the polymerization of 
vinyl compounds. If there is no chain transfer agent 
present, the polymerization continues until termination by 
disproportionation or combination occur. In the presence of 
a mercaptan, termination can occur through chain transfer. 

The hydrogen from the sulfhydryl group of the mercaptan 
is readily extractable. A propagating polymer chain can 
thus react with the mercaptan (Step 3) , terminating 
propagation and leaving a sulfur radical on the mercaptan. 
If the concentration of mercaptan is high, the mercaptan 
itself can react with the AIBN radical (Step 4), also giving 
a sulfur radical. The resulting sulfur radical can then 
initiate the free radical polymerization of a vinyl monomer 
(Step 5) . 

If the mercaptan contains hydroxyl or carboxylic acid 
functional groups (R' ) , the initiating sulfur radical 
introduces functionality to one end of the macromolecule . 
The growing functionalized polymer radical can again react 



11 



AIBN 



, CH 3 -C-N=N^-CH 3 -A* 2CH 3 ^ N + N 9 
CH 3 CH 3 CH 3 2 



C s N monomer polymerization 
ch 3 -<:. + =i -► 

CH 3 R 



•"^lA^VVSA^^i^VAV-WVW^-JVAVAW^- # 



r=N mercaptan C=N 

4 CH 3 -2- + H:S-R' CH 3 -<:H + R' S . 

CH 3 CH 3 



5 R'S- + — [ " R 

R 



Figure 2.1 Mechanism of f unctionalization using chain 
transfer agents. 



12 



with the mercaptan (Step 6) yielding a terminated 
functionalized chain and another molecule of sulfur radical 
which can react with more monomer (Step 5) to form a 
reaction loop. The effectiveness of f unctionalization is 
dependent on the chain transfer constant of the mercaptan as 
well as the relative concentrations of mercaptan, monomer, 
and free radical initiator (Tsu91). The AIBN concentration 
is kept extremely low relative to the chain transfer agent 
to minimize the number of chains initiated by the AIBN. Any 
chains initiated by AIBN will be non-functionalized (see 
Steps 2 and 3) . 

The advantage of this chain transfer method is that it 
can be used with a wide variety of vinyl monomer systems. 
Macromonomers composed of any monomer which can be 
polymerized free radically should be able to be synthesized 
using this method. Also, macromonomers which themselves are 
random copolymers also become feasible. 

The resulting functionalized macromolecule can be 
utilized in two different ways. As with the anionic 
macromonomers, the resulting hydroxyl or carboxylic acid 
monofunctionality can be converted to a methacrylate or 
vinyl functionality for further polymerization with vinyl 
monomers (Alb86, Che91, Tsu91) . Chen and Jones (Che91) have 
synthesized hydroxyl functionalized polyacrylates using 
mercaptoethanol as the chain transfer agent. Similarly, 
Albrecht and Wunderlich (Alb86) have synthesized hydroxyl 
terminated PMMA with Mw of 6500- 23000 g/mole. Both studies 



13 



have indicated that high levels of f unctionalization are 
realized. The hydroxyl group in each case was converted to 
a vinyl functionality through reaction with isocyanatoethyl 
methacrylate . Tsukahara et al. (Tsu91) have synthesized 
carboxylic terminated PMMA using mercaptoacetic acid as the 
chain transfer agent. The acid functionality was reacted 
with glycidyl methacrylate to produce methacrylate end 
capped PMMA. 

These routes produce methacrylate terminated polymers 
which can be subsequently polymerized with a vinyl monomer 
similarly to the anionically polymerized macromonomer . In 
order to synthesize graft copolymers, these macromonomers 
are dissolved in a solution containing a different vinyl 
monomer as well as a free radical initiator. Graft 
copolymers of a wide range of monomers can be synthesized in 
this fashion (Che91) . But this macromonomer chemistry has 
generated graft copolymers mostly limited to vinyl-vinyl 
type systems (Nai92) . 

The functionalized amine, hydroxyl or carboxylic acid 
terminated macromonomer can also be used without the vinyl 
functionalization by direct coupling with other condensable 
terminated macromonomers to form block copolymers (Imi84) . 
For example, amine-terminated poly (methacrylates ) and 
polystyrene have been synthesized using mercaptoethyl 
ammonium chloride as the chain transfer agent (Imi84, 
DeB73) . Block copolymers of these macromolecules with 
carboxylic acid terminated polymers were synthesized by a 



14 



coupling reaction. However, due to the monofunctionality of 
the macromonomer, coupling produced only very low molar mass 
A-B type block copolymers. 

Another interesting use of chain transfer agents for 
graft copolymerization is one developed by Moraes et al. 
(Mor96) . They modified an ethylene-vinyl acetate (EVA) 
copolymer by hydrolysis and subsequent esterif ication with 
mercaptoacetic acid. This produced a sulfhydryl containing 
polymer backbone. In essence, this is a polymeric chain 
transfer agent. Methyl methacrylate (Mor96) and styrene 
(Bar96) were polymerized in the presence of the mercapto- 
modified EVA to give poly (EVA-g-methyl methacrylate) and 
poly (EVA-g-styrene) graft copolymers. 

Again, the described macromonomers and graft copolymers 
have been mostly limited to addition-addition copolymers. 
There are only a few cases in which addition type 
macromonomers have been graft copolymerized with 
condensation type monomers (Yam81, Chu82, Chu84, Chu88a) . 
In order for the macromonomers to be capable of undergoing 
condensation reactions in the production of graft 
copolymers, they must be dif unctional . This does not imply 
that each end of the polymer is f unctionalized . Instead, one 
end of the polymer contains a difunctional reactive group. 

Only two research groups have reported the synthesis of 
difunctional macromonomers using chain transfer agents. 
Nair (Nai92) has demonstrated the free radical chain 
transfer polymerization of styrene and various acrylates in 



15 



the presence of mercaptosuccinic acid. Dicarboxylic acid 
terminated polymers were synthesized in a range of molecular 
weights from 1 to 10 kg/mole and were shown to be highly 
f unctionalized. 

Yamashita et al. (Yam81, Chu82, Chu84, Chu88a) carried 
out brief studies on the preparation of dicarboxylic acid as 
well as dihydroxyl functional macromonomers of various 
methacrylate monomers. They also employed mercaptosuccinic 
acid as well as thioglycerol in the macromonomer 
preparation. The structures and resulting macromonomer 
structures for each of the chain transfer agents discussed 
are illustrated in Figure 2.2. 

The work by Yamashita is the most closely related to 
our synthetic approach: the evaluation of cysteine as a 
chain transfer agent in the synthesis of amino acid 
terminated macromonomers. Our survey of the literature 
found no mention of amino acid terminated macromonomers. 
2 . 1 . 1 . 3 .Modeling chain transfer reaction 

The first step in the use of chain transfer agents is 
the determination of the chain transfer constant. Knowledge 
of the chain transfer constant allows us to predict such 
critical variables as molar mass and functionality (Nai92). 
The chain transfer constant can be determined using the Mayo 
model (Ros82, Nai92) . The variation of the degree of 
polymerization for a free radical chain transfer 
polymerization is given by 



16 



Mono functional Chain Transfer Agents 



o 

HS— CH 2 -C-OH »► 

HS— CH 2 -CH 2 -OH >■ 



CH 3 



CH 2 
reactive methacrylate 



\\S CH^~CH? — NHolHCl &* lAMAAAftWWWSAAA/WMMAA*^^ 



Difunctional Chain Transfer Agents 



HO— CH 2 — CH 2 -CH 2 -OH 
SH 

O O 

HO-C— CH 2 -CH 2 -C-OH 

k 



OH 



AAAMAAWAAMMAAAMA/SWAAAAWrtAAWWWWVW 



OH 
COOH 



AWMW*WIWWM*W«««M«W»WW 



COOH 



Figure 2.2 Schematic illustration of utilized chain 
transfer agents and macromonomers thereof 



17 



f K *, 



DP,, 






+ Cs 



(2.1) 



where Cs = Chain transfer constant = k tr ansfer/k p 
[S]= Chain transfer agent concentration 
[M]= Monomer concentration 
DP n = Degree of polymerization 
k t ,k p ,Rp= rate constant for termination, 
propagation, and the rate of polymerization 
respectively . 

The degree of polymerization in the absence of chain 
transfer to transfer agent, DP no , can be described by 
eguation 2.2 where 



1 



DP,, 



k 2 p [Mf 



(2.2; 



Substituting this value in equation 2.1 gives us the Mayo 
equation (2.3) for prediction of the chain transfer constant 
where 



1 



DP,, DP,, 



1 +r [s] 



[M] 



2.3: 



This equation is valid only when the initiator 
concentration is low. By synthesizing a series of polymers 
with different ratios of chain transfer agent to monomer, a 



IS 



Mayo plot can be used to determine the Cs . Knowledge of the 
Cs for a particular system enables one to adjust the 
reactant concentrations in order to target a specific molar 
mass polymer. 

The Mayo model can also be used to predict the 
functionality of the polymer obtained. If we multiply both 
sides of equation 2.3 by DP n , we get 



DP,, [S] 

\ = =- + DP, l Csj-j- (2.4) 

DP,,,, [ M\ 



where the two terms on the right represent the fraction of 
unfunctionalized and f unctionalized chains. If the value of 
Cs and therefore the rate of chain transfer is high, 
termination occurs primarily by chain transfer and high 
rates of functionalization are expected. The extent of 
functionalization also increases with increasing mercaptan 
content. If a lower concentration of chain transfer agent 
is used or if a lower value of Cs is observed, the 
probability of termination through other methods such as 
disproportionation or combination increases. As other 
termination mechanisms become more prevalent, the extent of 
functionalization decreases. 

It is important to note the limitations of the Mayo 
model. This model is valid only under certain assumptions 
(Ath77, Nai92) . The first of these is that chain transfer 
occurs exclusively to the chain transfer agent. In 



19 



practice, however, some chain transfer to solvent and 
initiator is generally observed. Also, these values, as in 
the case of copolymer reactivity ratios, are valid at 
instantaneous conditions. In other words, low conversions 
are desired in order to limit the composition drift between 
the monomer and chain transfer agent. With these 
assumptions in mind, determined values of Cs and predicted 
functionalities are only estimates or theoretical 
predictions assuming ideal conditions. 

2 . 1 .2 . Polyamide Addition-Condensation Multiphase Copolymers 

A variety of polyamide containing graft and block 
copolymers are described in the literature. Our specific 
interest lies in the ability to graft or block copolymerize 
polyamides with addition polymers such as methacrylates and 
other olefinic monomers. Several approaches have been taken 
in the synthesis of these structures. The benefits and 
limitations of each approach are described herein. 
2 . 1 .2 . 1 .Poly (amide-b-olefin) block copolymers 

Anionic block copolymerizations . The first evidence in 
the literature of block or graft copolymerizations of vinyl 
monomers with polyamide were found in the patent literature 
(Fur63, Bak65, God69) . The synthetic approach taken in 
these investigation involved the sequential anionic 
polymerization of a vinyl monomer and an isocyanate. 
Specifically, Godfrey (God69) showed that anionically 



2 



polymerized 'living' polystyrene, polyisoprene, and 
poly (methyl methacrylate) could initiate the polymerization 
of butyl isocyanate. The resulting product can be thought 
of as a N-butyl nylon 1-b-olefin block copolymer. The 
mechanism of block copolymerization is illustrated in Figure 
2.3. High molar mass block copolymers were formed with 
polydispersities ranging from 1.2 to 1.6. Although this 
reaction was successful, the choice of polyamide in this 
synthesis is limited due to the isocyanate precursors. All 
block copolymers involving isocyanates will form nylon 1 
type polyamides. Also, the choice of olefinic monomer is 
also limited to the previously mentioned limitations of 
anionic polymerizations. 

Macroinitiators for lactam polymerization . The 
majority of the literature concerning polyamide block 
copolymers involves the anionic copolymerization of 
caprolactam (Pet79, Ste82, Bor88, Mou93, YnM94), the 
precursor to nylon 6. The first step in these 
copolymerizations is the synthesis of polymeric 
macroinitiators from the desired vinyl monomer. The end 
group must be suitable for the initiation of the anionic 
polymerization of caprolactam. The most recent example 
involves the block copolymerization of amine-terminated 
butadiene nitrile copolymer (ATBN) with caprolactam (YnM94). 
The amine group is reacted with terephthaloyl biscaprolactam 
to form a polymeric activator. Upon addition to a 



21 



Bu: Li 



.-t 



+ 



~1 



Anionic 'living' polymer 
Bu— (CH 2 -CH)x-CH2-CHfLi + 

k k 



Bu— (CH 2 -CH)x-CH2-CH: Li + 

k k 



isocyanate 

() 

C=N - 

k 



Amide- Vinyl 
block copolymer 

II 
hCH 2 — CH--C-N — 

r * R- y 



Figure 2 . 3 



Mechanism of block copolymer formation through 
sequential polymerizations of vinyl monomer and 
isocyanates . 



22 



caprolactam solution containing additional initiator, A-B-A 
type block copolymers are formed with a ATBN center block. 
The molar masses of the resulting copolymers were not 
evaluated. Studies of the block copolymers concentrated on 
their microstructure and mechanical properties. 

Similar block copolymerizations were run using ester 
terminated polystyrene and isocyanate terminated 
polybutadiene (Pet79) and isocyanate terminated 
polyisobutylene (Won82). Both end groups can react with 
caprolactam to form a macroinitiator for the polymerization 
of nylon 6. A schematic of this macroinitiator formation 
and block copolymerization is illustrated in Figure 2.4. 
Spectroscopic evidence of A-B block copolymer structure is 
shown. However, signif icanthomopolymer formation, i.e., > 
30%, was observed due to coupling reactions between two 
functionalized macroinitiator molecules. 

Although some success has been demonstrated using the 
macroinitiator method, several limitations exist. One 
limitation of this approach is that this mechanism is 
restricted to the polymerization of lactam based polyamides. 
More importantly, Stehlicek (Ste77) and Hergenrother (Her74) 
have reported that synthetic approaches that employ the 
anionic polymerization of lactams activated by 
macroinitiators are handicapped by the occurrence of side 
reactions that may yield insoluble, crosslinked product. 



2 3 



Hydroxyl terminated Hexamethylene diisocyanate Isocyanate terminated 

polymer polymer 



° o o o 



1 _^h 2 ^H^)H C=N-<CH 2 ) 6 -N=C - ^CH 2 -CH^O Jj-NH-CCH^-N J 



■1 



Caprolactam 
o o o 

2 -^CH 2 — CH^O-C-NH-(CH 2 ) 6 -N=<!! + NH— C 

(CH& 



I X & 



Caprolactam terminated Ny)on fi b , Qck copolymer 

o P ol y mer o o 

3 -(C^-CH^JI-NH-tCH^-NHJ-N-^ + NH ^I J^ _^^HVAH- ( CI4)5^-k 



Figure 2.4 Reaction schematic for macroinitiator formation 
and subsequent anionic block polymerization of 
caprolactam. 



24 



Functional polyamide macroinitiators . The synthetic 
routes for block copolymerization previously described 
utilize anionic polymerization methods. One interesting 
twist on the macroinitiator method is to synthesize 
polyamide macroinitiators (Cra80, Cra82, Den89) . These 
polyamides contain functional groups which, under 
stimulation from light or heat, can dissociate into 
macroradicals . Thus, these macroinitiators are capable of 
initiating the free radical polymerization of vinyl 
monomers . 

Two distinct routes have been reported. The first 
(Cra80, Cra82) involves the modification of aliphatic 
polyamides such as nylon 6 and nylon 6,10. The reaction 
schematic for polyamide modification and subsequent block 
copolymerization is illustrated in Figure 2.5. The 
secondary amines in the polyamides can be nitrosated using a 
variety of nitrosating agents including nitrous acid and 
dinitrogen trioxide. The resulting N-nitrosoamines can 
rearrange to form a diazo linkage. Diazo compounds are well 
known as free radical initiators (Ros82) . The polyamide can 
then, under exposure to heat (Cra80) or light (Cra82), 
decompose into macroradicals and initiate the polymerization 
of olefinic monomers. Block copolymers of nylon 6 and nylon 
6,10 with MMA, styrene, vinyl acetate and styrene- 
acrylonitrile have been synthesized by this method. 

The second route to polyamide macroinitiators (Den89) 
also involves the introduction of dissociative azo linkages. 



25 



Aliphatic polyamide Nitrosated polyamide 



1 **wC — NH'»««««««*«wC — NH*«» + N2O3 >■ vwwC — N(NO)"*«^*«*»««»<? — N(NO)< 



Diazo ester modified polyamide 

■N(NO) AVW,ftwwwv,w *'C — N(NO)* 



00 00 

2 J_ N ( NO )- W wvwv»«v^-N(NO) ■* ^^_N=N~*~~~~»»C-0-N=N 



Polyamide macroinitiators 

3 AVWC O— N =N <WWWVWMMWC— O — N =N * W ~~^ *" ■ M * WWMMWW * ,< ""«"*^«"* •■W^**»W«* 

-N 2 , -C0 2 



Olefinic 
monomer A-BandA-B-A 



=1 amide-olefin block copolymer 



^wwwvsw^. • . Nylon Qjeft] Olefin Nylon Olefin 



Figure 2.5 Reaction schematic of block copolymerization 
initiated by nitrosated polyamide 
macroinitiators . 



26 



The difference is that the azo linkages are introduced 
during the polyamide synthesis. Denizligil showed that 
dinitriles can react with formaldehyde in the presence of 
strong acids to form a polyamide. The reaction schematic is 
illustrated in Figure 2.6. 

Specifically, AIBN was copolymerized with formaldehyde 
in the presence of sulfuric acid. AIBN is of interest 
because it has both dinitrile functionality as well as a 
labile azo functionality which can decompose to free 
radicals under heat. The resulting polyamide was used to 
initiate the polymerization of MMA and styrene in a 
DMSO/methylene chloride solvent system. 

Although block copolymers were formed by both processes 
outline above, no account was given as to the extent of 
degradation of the polyamide. These polyamide 
macroinitiators function only through their ability to 
degrade. That is, block copolymerization occurs through the 
chain scission of the polyamide. The extent of chain 
scission, especially in the AIBN based polyamide which has a 
very low molar mass between azo groups, could severely deter 
application of this process. 

Coupling of low molar mass reactive polymers . The 
synthesis of block copolymers from the coupling reaction of 
prepolymerized polyamide and polyolefin with reactive end 
groups has also been investigated (Mas79, Ima84, Kim92). 
Synthetically, this is the least complicated method of block 
copolymer synthesis. For example, Imanishi has reacted 



2 7 



Ns=C 



AIBN 



CH 3 

I 



-N=N- 



CH 3 



CH 3 



CH 3 



=N + 



() 

II 

HCH 



H 2 S0 4 



Azo functional polyamide 



O CH 3 CH3O 



-NH 2 — C— C— N=N 
CH 3 



CH 3 



-NH-CH 2 4 



O CH 3 



CH 3 O 



-NH, 



-N=N- 



CH 3 



CH 3 



Polyamide macroinitiator 



-NH-CH 2 4 



-N 2 



• MVMWvVAWAVW • 



Polyamide macroinitiator 



Olefinic 
monomer 

n 



A-B-A 
block copolymer 

Olefin Amide Olefin 



Figure 2 . 6 Reaction schematic of AIBN containing polyamide 
and block copolymer thereof. 



28 



amine terminated polystyrene with terminally haloacetylated 
polyamides to produce a polystyrene-polyamide block 
copolymer. Although some block copolymer is formed using 
this type of coupling reaction, this method is characterized 
by the highest level of homopolymer contamination and 
product heterogeneity. 
2 . 1 .2 .2 . Poly (amide-g-olefin) graft copolymers 

The majority of the literature on amide-olefin graft 
copolymers in concerned with one of two topics- the grafting 
of vinyl monomers onto polyamide substrates through high 
energy processes or the formation of in situ graft 
copolymers at the interface of polymer blends. 

Grafting onto polyamide substrates . Various methods 
have been used to graft olefinic polymer chains off the 
backbone of prepolymerized polyamides. The method most 
often and most recently employed is through the use of high 
energy processes such as UV irradiation (Bog93, You95) , 
severe oxidation/peroxidation (Ela92, Buc96a, Buc96b) , 
gamma irradiation (Mue93, Mis96) , and plasma grafting 
(You95, Lee97) . 

In all of these cases, grafting is surface directed. 
Polyamide fibers, films, and membranes are subjected to some 
form of radiation or oxidation. High energy processes are 
used in order to form radical or ions at the polyamide 
surface. These radicals can initiate the polymerization of 
vinyl monomers to form a grafted surface. 



2 9 



The majority of these studies involve the grafting of 
hydrophilic monomers such as acrylic acid and acrylamide 
onto polyamide surfaces. One exception is the study by 
Elangovan (Ela92) which has shown the grafting of PMMA onto 
wool fibers through the oxidation and subsequent redox 
initiation of MMA. This was done to improve the acid and 
alkali resistance of the fibers. Various other applications 
for these types of graft copolymers have been targeted 
including the production of pH responsive membranes (You95, 
Lee97, Mis96) , antibacterial fibers (Buc96a, Buc96b) , and 
new media for affinity chromatography (Mue93) . 

These processes are useful for their intended 
application, i.e., surface directed grafting. Well defined, 
isolatable graft copolymers are not synthesized by this 
method. In fact, radiation grafting is usually accompanied 
by significant crosslinking at the substrate surface as well 
as in the graft copolymer layer (Arn97) . 

In situ graft copolymers . As mentioned previously, 
graft and block copolymers can be added as a compatibilizer 
to immiscible polymer blends in order to improve the overall 
blend mechanical properties. To this effect, the greatest 
concentration of research in the synthesis of amide-olefin 
graft copolymers is in the area of melt compatibilization . 
This method may also be the most industrially applicable due 
to the simplicity of the process as compared to the more 
elaborate and labor intensive block copolymerization 
methods . 



30 



Graft copolymers can be formed in situ, during the melt 
blending of polyamides and polyolefins, if the polyolefin is 
functionalized with a reactive group. Specific examples 
include the modification of polyolefins with maleic 
anhydride (Maj92, Osh92, Mod93, WuC93, Maj94a, Maj94b, 
Gon95a, Gon95b, Gon95c, Sea95), glycidyl methacrylate 
(Chi96) and oxazoline (Bec96) . 

Glycidyl methacrylate and oxazoline have been copolymerized 
with styrene. These copolymers have been blended with 
polystyrene and nylon 6 to compatibilize the blend. The 
randomly dispersed oxazoline and epoxide functionalities 
within the styrene copolymer can react, during melt 
processing, with amine end groups from the polyamide. This 
results in a polyamide-g-polystyrene at the blend interface. 
Both studies (Chi96, Bec96) show reduced phase size in the 
blend as well as improved mechanical properties. A schematic 
of this reaction is illustrated in Figure 2.7. 

The most widespread use of the in situ technique for 
polyamides graft copolymers involves maleic anhydride 
modified polyolefins. Immiscible polyamide blends with 
polyethylene, polypropylene, and S-B-S block copolymers have 
been compatibilized using maleic anhydride (Maj92, Osh92, 
Gon95a, Gon95b) . In general, polyolefins such as 
polyethylene can be modified by grafting of maleic anhydride 
in the presence of free radical initiators (Sea95). The 
resulting anhydride functionality on the polyolefin can 
react with polyamide end groups at high temperatures during 



3 1 



1 



Poly(styrene-co-glycidyl methacrylate) Nylon 6 

ch 3 o 

W*WWWW« r CH? CH-T CH? (J*MMMM*MMMMMWWM<VWWVVW + NI - ^ - nC^^ C NH - " T 

c=o 

c. 

CH 
CH?° 




A 



extrusion 
+ polystyrene 



Poly(styrene-graft-nylon 6) + unreacted nylon 6 + polystyrene 



-£<;h 2 — ch-^— ch 2 -c 



ch 3 



^WMWWWWWWWWWWWWWWWWWM 




c=o 

c. 

c 

c 



H 2 

H-OH 

H 2 



NH 



compatibilized blend 



Nylon 6 




Figure 2.7 Reaction schematic of in situ graft copolymer 

formation from glycidyl methacrylate copolymers 



32 



extrusion of the blend. A schematic of this reaction is 
illustrated in Figure 2.8. 

The synthesis and application of in situ polyamide 
graft copolymers has been shown to be extremely effective at 
improving the phase dispersion within a variety of polymer 
blends. However, these graft copolymers have not been 
isolated and studied separate from the blend. This is due 
in part to the crosslinking that can occur during the graft 
reaction (Sea95) due to reaction of both ends of some 
polyamide chains. 

Macromonomer approach to amide-olefin graft copolymers . 
Previous work in the area of a macromonomer approach to 
polyamide graft copolymer synthesis is of particular 
interest. Free radical routes such as chain transfer 
f unctionalization offer more flexibility in monomer 
selection than anionic macromonomer synthesis. However, as 
mentioned previously, most of the previous work using either 
macromonomer method has been directed at the synthesis of 
vinyl terminated polyolefins and thus addition-addition 
graft copolymers. 

In order to synthesize graft copolymers from polyolefin 
macromonomers, the macromonomer must contain a dif unctional, 
condensable end group. For the synthesis of polyamide graft 
copolymers, these functional groups must be composed of acid 
or amine functionalities. Only Yamashita et al. (Yam81, 
Chu82, Chu84, Chu88a) have reported the graft 



33 



Maleated high density 
polyethylene (HDPE) 



Nylon 6 



rfMMMMWMMWM fc CH-) ("'{-I ) QU,--/^|-KWAMWMMAAM*rtWAM^ftWAMW -f- NH? - ttCHo)^ C NH^T" 



A 



o 




o 



o 



y extrusion 
+ HDPE 



2 Poly(ethylene-graft-nylon 6) + unreacted nylon 6 + HDPE 



-6-CH 2 — CH->— CH 2 -CH 



AMAAMMMMMMMMMMVWVVMMAV 



CH— CH 2 
/ \ 



o=c 



I 



NH OH 



Nylon 6 



compatibilized blend 



HDPE 



HDPE 




Nylon 6 



Figure 2 . 8 



Reaction schematic of in situ graft copolymer 
formation from maleic anhydride modified 
polyolef ins . 



34 



copolymerizations of such macromonomers, dicarboxylic acid 
terminated poly (methacrylates ) , with polyamide precursors. 
They employed mercaptosuccinic acid (Figure 2.2) as a 
chain transfer agent in the preparation of PMMA and 
poly (hydroxyethyl methacrylate) macromonomers. 
Macromonomers were copolymerized with aromatic diamines and 
diacids to form graft copolymers. One limitation of this 
approach is the stoichiometry . The degree of polymerization 
in condensation reactions is controlled primarily by 
conversion and stoichiometry as defined by Caruthers' 
eguation (Ros82) : 

\ + r 



Dp n«— r (2-5: 



where r is the stoichiometric ratio of reactive functional 
groups. This eguation is valid under the assumption of 
complete conversion. 

Determining the relative concentrations of amine and 
carboxylic acid groups is complicated by the introduction of 
macromonomers. The amount of dicarboxylic acid added in the 
reaction by Yamashita must be reduced to account for the 
acid end groups on the polymer and determining the exact 
amount of dicarboxylic acid becomes complicated. 
Macromonomers with built in stoichiometry, that is, with one 
amine and one carboxylic acid group, would be preferred. 
The precise stoichiometry of amino acid terminated 



35 



macromonomers becomes especially beneficial either for 
grafting with amino acids or for maximizing of graft 
copolymer molar mass. 

Also, only high Tg poly (methacrylate) dif unctional 
macromonomers were synthesized. There is no evidence in the 
literature of these type of graft copolymers containing a 
low Tg rubbery phase as investigated in this study. 

An interesting twist on the macromonomer approach to 
amide-olefin graft copolymers was developed by Izawa et al. 
(Iza93) . They synthesized vinyl f unctionalized polyamide 
macromonomers which could be free radically polymerized with 
vinyl monomers. A polycondensation of aromatic amino acids 
was run in the presence of methacrylic acid and p- 
carboxystyrene chain terminators. Complete consumption of 
the macromonomers during the free radical graft 
copolymerization with MMA revealed almost complete 
functionalization in the macromonomers. Although this 
method resulted in vinyl functionalized chains, the molar 
mass of these macromonomers is about 600g/mol. This low 
molar mass can be explained by the stoichiometric imbalance 
caused by addition of the end capping agent. 

2.2. Polymerization Shrinkage in Dental Composites 

Polymer based dental composites are replacing amalgam 
as the material of choice for dental restorations. The 
major drive toward the use of polymer based systems is based 



36 



on the aesthetics of the restoration. Composites compare 
favorably with silver amalgam in this aspect. However, the 
acceptance of composites is hampered by certain property 
limitations. The evolution of developments in these 
materials is described below. 

2 . 2 . 1 . History of Dental Composites 

The evolution of dental composites represents a logical 
sequence of developments based upon current technologies 
well known to the non dental community. The first acrylic 
filling materials were used at the time when polymer science 
was a young immature science whose growth was largely due to 
World War II and the need for synthetic rubber and a non 
breakable canopy for fighter planes. The early polymer 
based restoratives, based on methyl methacrylate monomer, 
exhibited large volumetric shrinkage, low mechanical 
strength, a high propensity for staining, high wear rates, 
marginal leakage and inflammatory tissue responses. None of 
the first generation materials had sufficient strength or 
adhesion to tooth structures to withstand the rigorous 
forces of oral function. 

The next generation of restorative materials were 
composites. The composites were based upon the 
incorporation of glass particles into the resin. The glass 
particles increased the mechanical strength and abrasion 
resistance and reduced total volumetric shrinkage simply by 



37 



reducing the content of resin in the restoration. In 
addition to the development of the composite materials, a 
new reactive methacrylate type monomer was developed by 
Bowen (Bow62) . Bowen's studies with epoxide resins led to a 
pivotal combination of the mechanical properties of the 
epoxy resin with the fast reacting methacrylate resin in the 
form of BisGMA. The first BisGMA systems introduced were 
polymerized by the chemical process wherein benzoyl peroxide 
is combined with a tertiary amine to form free radicals at 
room temperature. Later numerous variations of the light 
cured systems were introduced to the spectrum of dental 
materials including both UV and visible light activated 
materials. The UV light was scattered by the filler 
particles in the composites and thus the depth of cure was 
limited. The visible light activated restorations could 
achieve a greater depth of cure and thus have become the 
main system. 

In addition to the change in cure mechanism, numerous 
examples of modifications to the BisGMA structure and 
synthesis of other reactive methacrylate monomers (Lee89, 
Kaw89, Joh89, Ven93) have been reported. Most of the 
modifications involve either elimination of the hydroxyl 
group or modifications through esterif ications or 
substitution with urethane groups. There are slight 
improvements in both wet and dry properties as a result of 
modifications to BisGMA, however usually the differences are 



3 8 



not significant and many manufacturers still rely on the 
BisGMA monomer for their dental composites. 

The failure of these dental composites, and poor 
lifetime performance as compared to amalgam restorations, is 
generally attributed to a poor interfacial properties 
(Sod91) . Although the glass-resin interface has been 
studied extensively, the failure is usually attributed to 
the interface between the composite restoration and the 
remaining tooth structure. 

Two of the main sources of this poor interface are as 
follows : 

1) the polymerization shrinkage during composite cure 
causing the restoration to pull away from the remaining 
tooth structure (Bau82) . 

2) poor bonding between the exposed tooth structure, 
composed of hydrophilic proteinaceous dentin tubules, 
and the hydrophobic dimethacrylate composite (Sod91) . 

The volumetric shrinkage is due to the reduction in 
molar volume that occurs as vinyl monomers move from Vander 
Waals distances to covalent bond distances during 
polymerization. Volumetric shrinkage leads to poor marginal 
adaptation to the tooth structure which causes marginal 
leakage and recurrence of caries (Bra86) . Also, excessive 
stresses are generated in the restoration which create 
failures in both the remaining tooth structure and or the 
restoration depending upon the geometry of the restoration 
(Dav91). Shrinkage in current BisGMA based composite ranges 



39 



from 1 to 6 volume % (Sul93) . Variation may be attributed 
more to different glass loadings and varying levels of 
conversions than to any major resin development. 

2 . 2 . 2 .Reduction of Polymerization Shrinkage in Dental Resins 

There are many research programs focused on different 
chemical structures and processes that will reduce 
polymerization shrinkage (Bra92, Bye92, Sta91, Liu90). The 
main thrust in dentistry has been the spiro orthocarbonate 
(SOC) based systems which are the result of early pioneering 
work by Bailey (Bai72). The spiro orthocarbonate reaction 
involves a cationic dual ring opening mechanism which 
increases the molar volume of the polymer compared to that 
of the monomer. A general reaction schematic of spiro 
orthocarbonate polymerization is shown in Figure 2.9. 
Although zero shrinkage resins can be produced, deficiencies 
with this ring opening system include the slow cure 
kinetics, the inability to reduce shrinkage under non-ideal 
conditions and cost of the reactive monomer (Bra92, Bye92) . 
Typically, dental restorations can be cured within a few 
minutes whereas the spiro orthocarbonates are very slow 
reacting . 

These systems do provide some insight as to a logical 
step in the evolution of dental restoratives. The ring 
opening polymerization kinetics may be too slow, however, 



40 



SOC monomer 

r-O O- 



Cationic initiator 



/— O^ 



r -Q(~)~ r -£- R ^ ^^ r — - 



I 



o 



Poly(SOC) 



o 
propagation 

Y >— R R 



1 <X> 



O O— ' 



Figure 2.9 Mechanism of ring opening polymerization of 
spiro orthocarbonate monomers. 



4] 



the ring opening mechanism does provide a net increase in 
molar volume. 

The objective of this study is to determine if the 
combination of the rapid kinetics of the methacrylate resin 
with the ring opening of anhydride structures can be used to 
minimize the polymerization shrinkage. Specifically, cyclic 
anhydride functionality in the form of maleic anhydride was 
be incorporated into the dental restorative based upon 
propoxylated BisGMA resin. 

2. 2. 3. Use of Anhydrides in Dental Applications 

Anhydrides have received some attention in dental 
applications. However, the anhydride is used as part of a 
bonding agent and generally the ring opened form is 
generally present at the time of application. 

Peutzfeldt and Asmussen (Peu91) have shown that the 
addition of maleic anhydride to dentin bonding agents can 
increase the mechanical properties by nearly 300% when 
combined with a secondary amine containing monomer such as 
urethane dimethacrylate . Their studies demonstrate the 
ability of the maleic anhydride to increase mechanical 
properties, however, they fail to isolate the ring opening 
mechanism. By mixing maleic anhydride and other anhydrides 
with the primary amine or a hydroxyl containing monomer such 
as hydroxyethyl methacrylate (HEMA) , either an amide linkage 
or an ester linkage is formed. Thus, the ring opening 



4 2 



occurs prior to the polymerization reaction and hence has no 
influence on the volumetric shrinkage. 

Another example of the use of the anhydride structure 
in dental restorative materials is 4-META or 4- 
methacryloxyethyltrimellitate. Normally this reactive 
component is supplied in the dicarboxylic acid form and thus 
has no influence on polymerization shrinkage. It is however 
very effective in promoting adhesion to the enamel structure 
as well as numerous other substrates (Nak80) . The 
dicarboxylic acid structure of the 4-META monomer enhances 
the wetting or spread of the resin onto the tooth structure 
by lowering the surface energy of the exposed structure. 

2. 2. 4. Filler Modification in the Reduction of Overall 
Composite Shrinkage 

Methods involving reactions of the composite 
reinforcing phase have been evaluated as a possible method 
of offsetting polymerization shrinkage in dental composites. 
Liu et al. (Liu90) have used ammonia modified 
montmorillonite (MMT) as the reinforcing phase in BisGMA 
composites. At temperatures between 45 and 80°C, gaseous 
ammonia is released. The gas remains trapped within the 
reinforcing phase and causes dilation of the montmorillonite 
particles . 

Liu et al. have shown that polymerization shrinkage can 
be completely offset using this method in cold cure systems. 
However, this process has not been extended to directly 



4 3 



placed dental restorations. One possible reason is that the 
MMT functions due to the heat rise within the composite 
system that elevates the composite temperature. The heat 
rise in experimental systems using larger volumes of resin 
may be greater than the heat rise seen in actual dental 
restorations . 



CHAPTER 3 
MATERIALS AND METHODS 



3.1. Materials 



3 . 1 . 1 .Macromonomer Reactants 

Monomers used in the macromonomer synthesis included 
butyl acrylate, methyl methacrylate, and octaf luoropentyl 
methacrylate . The monomers were obtained from Aldrich 
Chemical Co. All were purified by fractional vacuum 
distillation (l-2mm Hg) and the middle 80% was collected. 
All monomers were stored under dry nitrogen over molecular 
sieves . 

The f unctionalizing agent used for the chain transfer 
polymerization was cysteine. Cysteine was also obtained 
from Aldrich and was used as received. Extreme care was 
taken to keep the cysteine stored under a dry nitrogen purge 
in order to prevent oxidation to cystine, the disulfide 
product of the oxidation. 

The solvents in the macromonomer synthesis, HPLC grade 
tetrahydrofuran (Fisher), ACS grade ethanol (Fisher) and 
Ultrapure™ water were used as received. HC1 was also used 
in the reaction. It was obtained from Adlrich as a ION HC1 
solution and diluted as reguired. Azobisisobutyronitrile 



44 



i 5 



(AIBN) initiator was obtained from Kodak and purified by 
recrystallization from ethanol . 

3. 1.2. Graft Copolymer Reactants 

Catalysts for the condensation polymerization, 
triphenyl phosphite and LiCl, were obtained from Aldrich and 
use without further purification. Care was taken to keep 
both of these hygroscopic chemical dry. They were stored 
under dry nitrogen and only opened within a drybox. 

Pyridine and N-methyl pyrrolidone were used as solvents 
in the graft copolymerization of the macromonomers with 
polyamide precursors. Anhydrous pyridine was purchased from 
Aldrich and kept continuously under dry nitrogen. Peptide 
synthesis grade N-methyl pyrrolidone (NMP) was obtained from 
Fisher, purified by distillation, and stored over molecular 
sieves . 

The amide precursors used in this study, p-aminobenzoic 
acid (ABA), adipic acid (AA) , and p-phenylenediamine (PhD), 
were obtained from Aldrich. ABA was used without further 
purification. AA was recrystallized from ethanol-water and 
PhD was recrystallized from ether. 

3. 1.3. Dental Monomers 

Monomers used in the modification of dental resins 
included propoxylated Bisphenol A glycidyl methacrylate 
(pBisGMA) , triethyleneglycol dimethacrylate (TEGDMA) , 2- 



46 



phenylethyl methacrylate (PEMA), and maleic anhydride (MA). 
All methacrylate monomers were obtained from Polysciences 
Inc. Maleic anhydride in the form of briquettes were 
obtained from Aldrich. 

TEGDMA and pBisGMA were purified by passing acetone 
solutions through Aldrich inhibitor removal columns, 
followed by evaporation at reduced pressure to remove the 
acetone. PEMA was fractionally vacuum distilled and maleic 
anhydride was recrystallized from benzene. AIBN initiator 
was purified by recrystallization from ethanol . 

3.2. Methods 

3 . 2 . 1 . Synthesis and Characterization of Macromonomers 

Synthetic procedure . Monomer concentrations in the 
polymerizations were maintained constant at 16wt.%. AIBN 
concentrations also remained constant at 0.1 mole % of the 
monomer concentration. Cysteine levels were varied in order 
to determine its affect on the polymerization of acrylates 
and methacrylates . 

In a typical polymerization, cysteine was dissolved in 
the prescribed amount of ION HC1 in a 200ml roundbottom 
flask equipped with a magnetic stirrer. Water and THF were 
then added in concentrations yielding a 50g solution of 
96.5/3/0.5 ratio, by weight, THF/water/HCl . lOg of monomer 
were added and the desired AIBN concentration was then 



47 



dissolved in the reaction mixture. A reflux condenser was 
attached to the flask. The reaction setup was then placed in 
a glycerin bath at 65°C and run for 6 hours under constant 
stirring. The isolation and purification of the various 
macromonomers synthesized is described in the corresponding 
results section 4.1.2, 4.1.3, and 4.1.4. 

Characterization of macromonomers . The molar mass 
distributions of the synthesized macromonomers were 
characterized by GPC using a Waters HPLC system including a 
Waters 600 Fluid Delivery Systems, a Waters 717 Autosampler, 
and a Waters 410 Differential Ref ractometer detector. Four 
Phenomenex crosslinked polystyrene columns with pore sizes 
of 10 5 , 10 4 , 500, and 100A° were used in series. The flow 
rate was 0.4ml/min. Sample concentrations were 
approximately 0.25% in HPLC grade THF. The injection volume 
was 50ul. All molar mass values were calculated using a 
polystyrene calibration curve. Anionically polymerized 
polystyrene standards were obtained from Polymer 
Laboratories . 

Transmission FTIR spectra of macromonomers were 
collected using a Nicolet 20SX spectrometer. 128 scans were 
collected for each sample at a resolution of 4cm" 1 . All 
liquids were run between KRS-5 crystals. Solids were run in 
transmission with KBr. 

NMR spectroscopy was performed using a 300MHz Gemini. 
The solvent used for macromonomer characterization was 



■•la 



deuterated chloroform. TMS was used as an internal 
standard. 64 acquisitions were collected for each sample. 

Elemental analysis for determination of C, H and N 
content was run on an Eager 200. 

ICP was run in order to determine the f unctionalization 
efficiency of the macromonomer synthesis. A Perkin Elmer 
Plasma 40 Emission Spectrometer was used and a wavelength of 
180.73nm was monitored. This wavelength was used to 
determine the sulfur content of the polymer. A sulfur 
standard was obtained from Fisher and diluted using 
volumetric flasks. 

Sample preparation for ICP involved making a 0.5 wt . % 
solution of the macromonomer in a 96/4 mixture, by weight, 
of water/triton X. Triton X was used as a surfactant in 
order to stabilize the emulsion of the poly (butyl acrylate) 
in water. Only the liquid, low Tg, macromonomers could be 
analyzed by this method. Stable emulsion of high Tg 
methacrylate copolymers could not be obtained. 

Sulfur content was determined in ppm in solution. 
Using the value of sulfur concentration in combination with 
the molar mass values we can calculate the extent of 
functionalization. The following is an example of one of 
these calculations. One mole of 2 . 6kg/mol poly (butyl 
acrylate), from GPC analysis, in which every chain is end 
capped by one mercaptan chain transfer agent residue will 
contain one mole of sulfur or 32g. Therefore, 32/2600 or 
1.23 wt . % . If the prepared solution contains 0.5 wt . % 



4 9 



macromonomer, the solution should contain 0.005*0.0123= 
62ppm of sulfur. Again, if every chain were functionalized, 
we should measure a sulfur concentration of 62ppm. Instead 
a concentration of 46ppm was measured. From this we 
estimate that 46/62 or 75% of all chains contain one sulfur 
molecule or 75% are functionalized. 

DSC analysis was performed using a Seiko DSC 220 
interfaced with a Seiko 6500H Rheostation. The analysis was 
performed at heating rate of 10°C/min under a continuous 
flow, lOOml/min, of dry nitrogen gas. On average, 10 mg 
samples were analyzed in crimped aluminum pans versus an 
inert sapphire reference. 

3 .2 .2 .Synthesis and Characterization of Graft Copolymers 

Synthetic procedure . Stoichiometric molar 
concentrations of amine and carboxylic acid groups were used 
with a total amount of reactants egual to 5mmol . Triphenyl 
phosphite was added at a 1:1 mole ratio of TPP : carboxylic 
acid groups. The amount of LiCl added was kept constant 
throughout as was the type and amount of solvent used. 

In a typical polymerization, 1 . 37g of 2 . 6 kg/mol p(BA) 
macromonomer (0.53 mmol), 0.241g (2.24 mmol) p- 
phenylenediamine, 0.326g (2.24 mmol) adipic acid, 1.55g TPP 
(5mmol), and 0.09g LiCl were dissolved in 30ml of an 80/20 
NMP/pyridine solution in a 100ml flask. All mass readings 
and component mixing was performed in a drybox. The 



bO 



reaction mixture was then heated at 100°C for 4 hours. The 
resulting polymer, a tacky light brown solid, was obtained 
almost quantitatively by precipitation in an excess of 50/50 
water/methanol nonsolvent, filtered, washed with methanol 
and dried overnight under vacuum at 40°C. 

Characterization of graft copolymers . Purification of 
the graft copolymers was done by Soxhlet extraction using 
HPLC grade THF. This was done in order to remove any 
homopolymer which may result from unfunctionalized 
macromonomers . Samples ranging from 0.8-1.0g were extracted 
to constant weight using a Whatman cellulose extraction 
thimble . 

The extractant solutions were diluted to appropriate 
concentrations for GPC analysis. The level of dilution 
required was dependent on the amount of material extracted. 
GPC was run with simultaneous detection using the 
differential ref ractometer described previously as well as a 
Waters 996 Photodiode Array UV detector. This detector 
allows one to get a full UV scan at each elution time. This 
affords the ability to determine structural differences 
between UV absorbing fractions within the solution. All 
other testing conditions were identical to those for 
characterization of macromonomers. 

Transmission FTIR spectra of the graft copolymers were 
collected using KBr with collection parameters equivalent to 
those described previously. 



51 



Elemental analysis and DSC methods were identical to 
those used in macromonomer characterization. 

The only difference in the NMR spectroscopy from that 
of the macromonomer was the solvent employed. Deuterated 
sulfuric acid was used as the solvent and the solvent peak 
from residual undeuterated acid was used as an internal 
standard. 

The synthesized graft copolymers were blended with 
commercial extrusion grade Nylon 6 from BASF and with blends 
of Nylon 6 with 65kg/mol poly (butyl acrylate) synthesized in 
this laboratory. Initial attempts were made to blend the 
polymers by dissolution in dichloroacteic acid followed by 
coprecipitation in methanol. After vigorously drying the 
resulting powders, films were compression molded at 230°C. 
This method was abandoned when the pure nylon 6 prepared in 
this manner showed severe embrittlement . Either residual 
acid caused degradation or the dissolution-precipitation 
step removed a stabilizer. 

The materials were then mixed in the solid state. In 
order to get the most homogeneous mixture of graft copolymer 
with Nylon 6 and graft copolymer with Nylon 6/Poly (butyl 
acrylate), the samples were mixed at cryogenic temperatures. 
A SPEX 6200 Freezer Mill was used at maximum impact 
freguency with the sample immersed in liguid nitrogen. All 
samples were milled for 8 minutes. The resulting powders 
were homogeneous in appearance. All blends were compression 
molded at 230°C between Teflon® coated polyimide films and 



52 



allowed to cool in the mold. The resulting films were 
approximately 0.2mm thick. 

Tensile properties of the films were measured using an 
Instron 1122 equipped with an 890 Newton load cell at 
ambient conditions. Five samples were tested for each 
material according to ASTM D638M. 



3_- 2 . 3 . Synt hes i s and Cha ract er i zation of Anhydride Modified 
Dental Resins 



Synthesis and sample preparation . An experimental 
matrix was prepared composed of varying anhydride, pBisGMA, 
and TEGDMA concentrations. Dental resin samples were 
prepared by dissolving the maleic anhydride in the dental 
methacrylate monomer compositions. 0.4 wt . % AIBN initiator 
was added to the solution. The resulting viscous solutions 
were transferred to a 2mm thick mold. The mold consisted of 
two glass plates lined with Teflon® coated polyimide film 
and a f luoropolymer elastomeric tubing to keep the solution 
in the mold. The solutions were cured under a dry nitrogen 
atmosphere at 75°C for 12 hours followed by a postcure at 
160°C for 2 hours. 

Linear copolymers of maleic anhydride with phenylethyl 
methacrylate were synthesized in bulk. The desired 
anhydride amount was dissolved in PEMA in a 15ml glass test 
tube and 0.4 wt . % AIBN was added. The solution was purged 
with dry nitrogen, sealed, and polymerized at 75°C for 4 
hours. The resulting polymer was isolated by dissolution in 



5 3 



chloroform and precipitation in ether. Samples were filterd 
and dried overnight under vacuum at 40°C. 

Characterization of anhydride copolymers . Equilibrium 
water content was measured using Ultrapure water. Samples 
were approximately 2mm x 5mm x 10mm. Samples were placed in 
an incubator at 37°C until a constant weight was reached. 
The swelling solution was then changed, adding fresh 
Ultrapure water and weight again monitored to insure all 
unreacted anhydride has been extracted. On average 
equilibrium was reached after 1-2 weeks. 

All weights were measured using a Denver Instruments A- 
200DS with readings taken to the fifth decimal place. 

Density measurements were taken using a Mettler 33360 
Density determination apparatus in combination with the 
Denver Instruments scale. The Archimedes' method was used 
and measurements ere taken at 25°C using Ultrapure® water. 
All samples were re-weighed after testing to insure that the 
time scale of these measurements were insufficient to allow 
the samples to absorb water. 

UV absorption spectroscopy was run on the extractant 
solutions in order to monitor the extraction of maleic 
anhydride. Actually, any extracted anhydride would be 
extracted as maleic acid due to hydrolysis. A calibration 
curve for absorbance versus concentration was made using 
standards. Standards were prepared in the expected 
concentration range by hydrolyzing and dissolving maleic 
anhydride in Ultrapure® water. A wavelength of 274nm was 



54 



used. Thus, by monitoring the absorbance at 274nm of the 
extractant solutions, concentrations of maleic acid could be 
determined. Knowing the volume of water used in the 
swelling experiments, we can calculate the mass of maleic 
anhydride extracted. Assuming all free anhydride was 
extracted, the anhydride not extracted is assumed to be 
incorporated. 

GPC, FTIR, and DSC of the linear maleic anhydride 
copolymers were run with parameters as described in the 
characterization of the polyamide graft copolymers. 



CHAPTER 4 
RESULTS AND DISCUSSION 



4.1. Synthesis and Characterization of Amino Acid-terminated 
Poly (acrylate) Macromonomers using Chain Transfer 

Chemistry 



The most prevalent synthetic route to well defined 
graft copolymers is through the use of macromonomers, low 
molar mass polymers containing a polymerizable end group. A 
review of the literature has shown that current studies, 
including those within this laboratory, have concentrated on 
synthesizing macromonomers which are polymerizable through a 
vinyl functionality. That is, they are polymerizable only 
with addition type monomers through a free radical 
mechanism. Because the macromonomers themselves are 
generally synthesized through either anionic or free radical 
polymerization in the presence of a f unctionalizing agent, 
the resulting graft copolymers which can be synthesized 
through this method are generally limited to addition- 
addition graft copolymers such as poly (styrene-graf t- 
acrylate) , poly (acrylate-graf t-methacrylate) , etc... 

It was the objective of this study to synthesize 
condensation polymerizable macromonomers, specifically amino 
acid terminated macromonomers, capable of reacting with 
amine and carboxylic acid groups in the synthesis of 



55 



56 



polyamide graft copolymers. An amino acid functionality is 
preferred over other end groups such as diacids or diamines 
due to the inherent stoichiometry that it provides . This 
stoichiometry is reguired in the condensation graft reaction 
to insure the highest degree of polymerization possible. 

The approach taken in this study involves the free 
radical polymerization of a vinyl monomer in the presence of 
a functional chain transfer agent (Ito77). Mercaptans, 
compounds containing a sulfur-hydrogen bond, are commonly 
used in chain transfer reactions. In fact, mercaptans are 
commonly used to control molecular weight in commercial 
polymerization reactors (Ros82). 

The mechanism by which functionalization can occur is 
depicted in Figure 4.1. Steps 1 and 2 are typical processes 
of free radical initiation. When exposed to heat, the AIBN 
breaks down into free radicals and nitrogen gas is evolved. 
The AIBN radicals can thus initiate the polymerization of 
vinyl compounds. If there is no chain transfer agent 
present, the polymerization continues until termination by 
disproportionation or combination occur. In the presence of 
a mercaptan or other chain transfer agent, termination can 
occur through chain transfer. The hydrogen from the 
sulfhydryl group of the mercaptan is readily extractable. A 
propagating polymer chain can thus react with the mercaptan 
(Step 3) , terminating propagation and leaving a sulfur 
radical on the mercaptan. If the concentration of mercaptan 



57 



AIBN 



, CH 3 -?-N=N-^-CH 3 -A_^ 2CH 3 ^ 
CH 3 CH 3 C 

C "N monomer polymerization 

! V* + 



' 3 



CH3 R 



^^*wwvw^**N»^S'Si«AN»ii»»«^Ai'vvviAf\'w 1 wi«vSi' 



r s]sj mercaptan C =N 

CH 3 -C- + H:S-R* CH 3 -^H + R - S . 

CH 3 CH 3 



^MWVWV>WWAA^^^^V^M^«V . 



5 R'S« + "H R' 

R 



Figure 4.1. Mechanism of functionalization using chain 
transfer reactions. 



58 



is high, the mercaptan itself can react with the AIBN 
radical (Step 4), also giving a sulfur radical. The 
resulting sulfur radical can then initiate the free radical 
polymerization of a vinyl monomer (Step 5) . 

If the mercaptan contains hydroxyl or carboxylic acid 
functional groups (R' ) , the initiating sulfur radical 
introduces functionality to one end of the macromolecule . 
The growing f unctionalized polymer radical can again react 
with the mercaptan (Step 6) yielding a terminated 
f unctionalized chain and another molecule of sulfur radical 
which can react with more monomer (Step 5) to form a 
reaction loop. The effectiveness of f unctionalization is 
dependent on the chain transfer constant of the mercaptan as 
well as the relative concentrations of mercaptan and free 
radical initiator (Tsu91) . The AIBN concentration is kept 
extremely low relative to the chain transfer agent to 
minimize the number of chains initiated by the AIBN. Any 
chains initiated by AIBN will be non-f unctionalized (see 
Steps 2 and 3) . 

Cysteine, a naturally occurring amino acid containing a 
sulfhydryl functional group, was evaluated as a chain 
transfer agent in the polymerization of acrylates and 
methacrylates . If cysteine were to act as an effective 
chain transfer agent, it would provide the desired amino 
acid functionality. 

Specifically, poly (butyl acrylate) and poly (methyl 
methacrylate-co-octafluoropentyl methacrylate) macromonomers 



b9 



were synthesized in the presence of cysteine. Poly (butyl 
acrylate) was chosen because it has a very low glass 
transition temperature, -54°C (Bra89), and therefore any 
graft copolymers containing it may be used as rubber 
modifiers. The f luoroacrylate copolymer was chosen because, 
due to the low surface energy of f luoropolymers in general, 
graft copolymers could be utilized as surface modifiers. 

4 . 1 . 1 . Determination of an Appropriate Solvent System 

A common solvent for both the monomer, either butyl 
acrylate or the f luoroacrylate-MMA mixture, and the cysteine 
chain transfer agent must be identified in order to insure a 
homogeneous solution during polymerization. Cysteine is a 
crystalline powder insoluble in common organic solvents. 
Solubility tests in the approximate concentrations required 
for synthesis of a 3kg/mole macromonomers were performed. 
As is shown in Table 4.1, at the appropriate concentrations, 
cysteine is insoluble in some common organic solvents which 
are suitable for the polymerization of butyl acrylate. Also 
butyl acrylate is completely immiscible with water, quickly 
separating into two layers. 



6 (J 



TABLE 4 . 1 Solvent determination for monomer and chain 
transfer agent 





Toluene 


THF 


DMF 


Ethanol 


n-Butanol 


H 2 


Cysteine 


i 


i 


i 


i 


i 


s 


Butyl 
acrylate 


s 


s 


s 


s 


s 


i 



Concentration of cysteine= 0.03g/5g solvent, 
lg/5g solvent. i= insoluble, s=soluble. 



Concentration of monomer= 



Because of the strong H-bonding interactions within the 
amino acid, it appeared to be necessary to add H 2 to 
disrupt crystalline structure. Cysteine was then pre- 
dissolved in water at high concentrations prior to the 
addition of THF. This method was successful in keeping 
cysteine dissolved in a THF/water mixture. One of two 
things generally occurred upon the addition of butyl 
acrylate. Either the concentration of water was too high to 
allow the butyl acrylate to dissolve, or the concentration 
was too low to prevent the precipitation of cysteine upon 
the addition of the acrylate monomer. It was determined, 
after much trial and error, that ethanol could be added in 
low concentrations in order to stabilize the 

THF/water/cysteine/butyl acrylate solution. The ethanol was 
effective in preventing the butyl acrylate from forming a 
second phase. The composition of the solvent system used 
was a 80/10/10 ratio, by weight, of THF/EtOH/H 2 0. The 
monomer concentration was 15 wt . % . 



6 1 



4 . 1 . 2 . Preliminary Studies of the Effectiveness of Cysteine 
as a Chain Transfer Agent in the Polymerization of Butyl 
Acrylate 



The synthesis of poly (butyl acrylate) in the presence 
of cysteine was carried out using the solvent system 
described above. Figure 4.2 depicts the desired amino acid 
functionality of the macromonomer . The 

monomer : cysteine :AIBN molar ratio used was 1000:30:1. The 
AIBN concentration must be kept low in order to minimize the 
number of chains initiated by AIBN. As stated previously, 
any chains initiated by the AIBN initiator and not the chain 
transfer agent will be in effect 'dead' chains. That is, 
they will lack the desired amino acid functionality. The 
polymerization was run under nitrogen at 65°C for 7 hours. 
A control polymerization was also run under the identical 
conditions in the absence of the cysteine chain transfer 
agent. The resulting polymers were isolated by rotary 
evaporation under vacuum at 40°C. Due its low glass 
transition temperature, poly (butyl acrylate) is virtually 
impossible to isolate by precipitation in a non-solvent. 
The reaction product of the control reaction was a clear, 
extremely tacky, viscous material with a yellowish haze. 
The cysteine modified product was very similar with the 
exception of the presence of a white precipitate dispersed 
within the poly (butyl acrylate). This precipitate could be 
separated from the polymer by dissolving the poly (butyl 



62 



butyl acrylate 



CH2=CH 

U 
i 

CH 2 
CH 2 
CH 2 

CH, 



+ 



cysteine 

o 

NH 2 -CH-C-OH 
CH2 

0.2wt%AIBN t 
65°C, 7 hrs. 

THF: EtOH :H 2 



O 
NH 2 — CH— C-OH 

CH 2 

i 



Poly(butyl acrylate) 



Figure 4.2 Schematic of ideal amino acid f unctionalization 
during polymerization of butyl acrylate. 



6 3 



acrylate) in THF. The precipitate was insoluble in THF and 
could therefore be collected by filtration. 

Gel permeation chromatography of p(BA) . Molar mass 
averages and distributions were measured using GPC in order 
to determine the effectiveness of chain transfer. Chain 
transfer should significantly reduce the molar mass of the 
resulting polymer. If cysteine were to have a chain 
transfer constant equivalent to other commonly studied 
mercaptans, it should drastically decrease the molar mass of 
p(BA) when compared to a neat polymerizaion . For example, 
similar concentrations of mercaptoethanol chain transfer 
agent have been used in this laboratory in the synthesis of 
hydroxyl terminated poly (styrene-acrylonitrile) . Using the 
Mayo equation described in section 2.1.1.3, we can calculate 
that mercaptoethanol (chain transfer constant=l . 1 (Zam95)) 
would yield an oligomer with a molar mass of @4kg/mol. 

The molar mass distributions of the control and 
cysteine modified P(BA) are shown in Figure 4.3. The number 
average molar mass (Mn) for the control sample was 63kg/mol, 
with a polydispersity index of 2.9. The product of the 
cysteine modified polymerization has an Mn= 19kg/mol. The 
molar mass was reduced, but not as much as would be expected 
if efficient chain transfer occurred. Also, the cysteine 
modified P(BA) has a much broader distribution, with a 
polydispersity index of 4.8. 

Analysis of GPC data . In order to properly explain 
these results, the presence of the side product of the 



64 



1 - 



> 

B 



- 



neat Poly(butyl acrylate) 
Mn=63Kg/mol Mw=186Kg/mol 
PDI=2.9 

PBA-cysteine pH=6.7 
Mn=19Kg/mol Mw=91Kg/mol 
PDI=4.8 



5 4 

LogMW 



Figure 4.3 



GPC results of preliminary butyl acrylate 
polymerizations . 



65 



cysteine reaction must be explained. The side product, with 
a melting point of @ 196°C, was determined to be crystalline 
by DTA (Figure 4.4). The FTIR spectra of this product, 
shown in Figure 4.5, shows the presence of a ester carbonyl 
at 1740cm" 1 . The broad absorption from 3400 to 2400cm" 1 
suggests the presence of a carboxylic acid functionality. 
Figure 4.6 shows the same spectra of the side product, 
focusing on the area from 1800 to 1500cm" 1 , as compared to 
butyl acrylate monomer. The side product does not have the 
sharp absorbance at 1640cm" 1 associated with the vinyl 
functionality in the butyl acrylate monomer. There is a 
broader absorption centered around 1580cm" 1 which is 
representative of an amine functional group. 

Upon investigation of the literature for possible 
explanations of this side reaction of cysteine, a study by 
Friedman et al. (Fri65) was found in which they investigated 
possible blocking agents for sulfhydryl groups in proteins. 
They showed that acrylates, in aqueous conditions, can react 
with cysteine through the sulfhydryl group. The S:H 
functional group can ionize under basic conditions into a 
sulfur anion according to their reaction pathway (Figure 
4.7). The sulfur anion then attacks the vinyl group of the 
acrylate. The resulting carbanion is immediately capped by 
a proton in the aqueous solution. 



66 



a 




50 100 150 200 250 300 350 400 



Temperature (°C) 



Figure 4.4 DTA trace of side product 



1.0 



67 




0) 


I 


o 


- 


c 


~ 


CD 


J 


-Q 


- 


k_ 




O 


- 


if) 


- 


£1 
< 


0.4 -! 



3000 2000 

Wavenumbers (cm-1) 



1000 



Figure 4.5 FTIR spectra of side product of cysteine 
modified P (BA) . 



68 



1.0 1 



-j ester carbonyl 
0.8 \ \ 



o 

c 

CD 
.Q 

o 

C/5 
-Q 



Side product of cysteine reaction 



amine 




1800 



1700 1600 

Wave numbers (cm-1) 



1500 



Figure 4.6 Comparison of FTIR spectra of side product with 
butyl acrylate monomer. 



69 



RSH + H 2 ^ RS- + H 3 + 
RS- + CH 2 =CH-COOR ■» RS— CH 2 — CH-COOR 
RS—CH 2 — CH-COOR + H 3 + -» a RS-CH 2 — CH 2 -COOR + H 2 Q 



Figure 4.7 Reaction pathway of cysteine with acrylates. 



When butyl acrylate is used, the product formed is 
S-carbobutoxyethylcysteine (Figure 4.8). According to 
Friedman, this compound has a melting point of 194-195°C, 
which is in good correlation to the T m of the side product, 
i.e., 196°C. Elemental analysis of the side product 
confirmed the correct chemical formula for S- 
carbobutoxyethylcysteine (Figure 4.8). 

In order to minimize or eliminate this side reaction, 
we must understand why it is occurring. In an aqueous 
solution, the ionization of the sulfhydryl group is an 
equilibrium reaction. It is the anionic form of cysteine 
which can react with butyl acrylate to form the side 
product. This equilibrium reaction has a pK a associated 
with it and therefore the relative concentrations of ionized 
to unionized species are influenced by the pH of the 
solution as governed by the Henderson-Hasselbach equation, 



pH = pK a + log 



[SH]. 



4.i; 



where [S-] is the concentration of sulfur anion and [SH] is 
the concentration of the unionized sulfhydryl group. The pK d 



70 



S-Carbobutoxyethylcysteine 

Nhfe-CH-C-OH 
6Hz 
S 

6H2 

6 

(Chfe) 3 

CHs 

Calculated wt.% for C 10 H 19 NO 4 S: 
C, 48.19; H, 7.63; N, 5.62 

Found: 

C, 48.47; H, 7.65; N, 5.51 



Figure 4.8 Structure and elemental analysis of side 
product . 



7 .1 



of the sulfhydryl group of cysteine is 8.3 (Voe90). In 
order to determine the relative concentration of ionized 
cysteine, the pH of the THF/EtOH/H 2 0/butyl acrylate/cysteine 
solution was then measured. The pH of the solution, 6.7, is 
below the pK a . Using equation 4.1, we can then determine 
that approximately 3% of the cysteine at a pH of 6.7 is 
present in the ionized form and therefore 3% is capable of 
reacting with butyl acrylate in the side reaction. 

If the effective concentration of chain transfer agent 
were only being reduced by 3%, we would expect that there 
would be sufficient unionized active cysteine to 
significantly affect the molar mass of the poly (butyl 
acrylate) . Again, in these chain transfer polymerizations, 
the molar mass is governed by the chain transfer constant as 
well as the relative concentrations of monomer, chain 
transfer agent, and free radical initiator. A 5% decrease in 
cysteine concentration would indicate that instead of a 
1000:32:1 monomer : cysteine :AIBN molar ratio, we would be 
working with a 1000:31:1 molar ratio which should still 
significantly decrease the molar mass of the poly (butyl 
acrylate) . One would expect a 5kg/mole instead of 4kg/mole 
macromonomer . 

The final mixture of products in this reaction depends 
upon the relative rates of cysteine consumption in the chain 
transfer reaction and the side reaction. Friedman has shown 
that the reaction between the sulfur anion and acrylates 
occurs almost instantaneously (Fri65) . On the other hand, 



72 



the polymerization of butyl acrylate occurs over a period of 
hours. The ionized cysteine is thus consumed at a higher 
rate than unionized cysteine. The desire for equilibrium in 
the ionization reaction (Figure 4.9) drives the reaction 
further to the right which leads to further ionization of 
cysteine and thus formation of more side product. Over 
time, the unionized cysteine concentration decreases until 
there is no cysteine present to cause chain transfer. 

The unexpected GPC results shown previously in Figure 
4.3 can now then be explained. At the early stages of the 
polymerization of poly (butyl acrylate), unionized cysteine 
is present at relatively high concentrations and low molar 
mass macromonomer is being produced. As time goes on, the 
cysteine concentration relative to butyl acrylate is 
decreasing leading to less termination through chain 
transfer and therefore larger molar masses. By the end of 
the reaction, all of the cysteine has been consumed by the 
side reaction and high molar mass poly (butyl acrylate) is 
being formed. This would explain the extremely broad molar 
mass distribution observed in the GPC analysis. More 
pertinent than the actual molar mass values is that in the 
absence of cysteine, initiation will come mainly from the 
AIBN and termination will occur by disproportionation 
(Bra89), leading to high molar mass unf unctionalized chains. 

Prevention of undesired side reaction . It is clear 
that in order to achieve complete chain transfer and 



73 



o o 

pKa=8.3 
NH 2 — CH-C— OH ^ NH 2 — CH-C— OH 



CH 2 
SH 



butyl acrylate 



Chain transfer 
functionalization 



H + 



CH 2 

T butyl acrylate 




S-Carbobutoxyethyl- 
cysteine 



Figure 4.9 Side reaction preventing complete chain 
transfer. 



74 



therefore produce highly f unctionalized macromonomers, side 
reactions must be reduced or eliminated. In order to 
prevent the formation of S-carbobutoxyethylcysteine, we must 
prevent the ionization of cysteine. By acidifying the 
polymerization solution, the initial concentration of sulfur 
anion can be virtually eliminated. For example, again using 
equation 4.1, if we were to acidify the polymerization 
solution to a pH of 1, the concentration of ionized cysteine 
would be reduced from 5% to 50 parts per billion. Although 
this ionized cysteine will still form the byproduct, the 
effective concentration of unionized cysteine will remain 
the dominant species. 

A new reaction was run under similar conditions to the 
previous cysteine modified polymerization with the addition 
of hydrochloric acid. The addition of HC1 facilitated the 
dissolution of cysteine. In fact, a homogeneous 
polymerization solution could be achieved in a solvent 
system containing 96.5/3/0.5 weight ratio THF/water/HCl . 
Because the concentration of water could be significantly 
reduced, the addition of ethanol was not necessary to keep 
the butyl acrylate monomer in solution. The pH of the 
reaction mixture was reduced to -0.76 and the reaction again 
was run for 7 hours at 65°C. At this pH, only lppb of 
cysteine is present in the ionized form. 

The resulting solution was neutralized with pyridine. 
Pyridine hydrochloride immediately began to precipitate and 
was filtered out. The poly (butyl acrylate) solution was 



75 



evaporated to dryness under vacuum at 40°C. The product 
yield was 52% of theoretical. Again a yellowish viscous 
liquid was isolated. The most significant visual difference 
between this product and those of the previous reaction was 
the much lower viscosity, evidence of lower molar mass 
polymer. Also there was no evidence of the formation of the 
S-carbobutoxyethylcysteine . 

GPC was run on the isolated product. Figure 4.10 shows 
the effect of acidification on the molar mass distribution 
of poly (butyl acrylate) . The concentration of cysteine was 
identical to that in the previous reaction. Yet, the molar 
mass and polydispersity of the poly (butyl acrylate) was 
significantly reduced, i.e., with an Mn of 2 . 6kg/mol and a 
polydispersity index of 2.3. The addition of HC1 allowed 
cysteine to participate in the chain transfer reaction. As 
was stated previously, if cysteine were to behave as 
effectively as other mercaptan chain transfer agents, a 
molar mass of 4kg/mol would be expected. 



4 . 1.3. Determination of Chain Transfer Constant of Cysteine 
in the Synthesis of Amino Acid- terminated Poly (butyl 
acrylate) Macromonomers 



The first step in the use of chain transfer agents is 
the determination of the chain transfer constant. Knowledge 
of the chain transfer constant allows us to predict critical 
variables such as molar mass and functionality (Nai92) . The 
chain transfer constant can be determined using the Mayo 



76 



1 - 



B 



o- 



neat Poly(butyl acrylate) 
Mn=63Kg/mol Mw=186Kg/mol 
PDI=2.9 

PBA-cysteine pH=6.7 
Mn=1 9Kg/mol Mw=91 Kg/mol 
PDI=4.8 

PBA-cysteine: HCI pH=-0.76 
Mn=2.6Kg/mol Mw=6.1 Kg/mol 
PDI=2.3 




6 5 4 

LogMW 



3 



Figure 4.10 Effect of acidification on chain transfer 
functionalization of poly (butyl acrylate) 



7 7 



model (Ros82). The variation of the degree of polymerization 
in a free radical chain transfer polymerization is given by 



1 



'*, *, 



DP,, 






+ Cs 



4.2) 



where Cs = Chain transfer constant 

[S]= Chain transfer agent concentration 
[M]= Monomer concentration 
DP n = Degree of polymerization 
kt,kp,R p = rate constant for termination, 
propagation, and the rate of polymerization 
respectively. 

The degree of polymerization in the absence of chain 
transfer, DP no , can be described by equation 4.3 where 



1 



DP n 



KM 2 



4.3) 



Substituting this value in equation 4.2 gives us the Mayo 
equation (4.4) for prediction of the chain transfer constant 
where 



1 



1 +r [S] 
= + Cs-, 



DP,, DP,, 



[M] 



(4.4) 



This equation is valid only when the initiator 
concentration is low. By synthesizing a series of polymers 
with different ratios of chain transfer agent to monomer, a 
Mayo plot (Tsu91) can be used to determine Cs to prove that 
cysteine is an effective chain transfer agent. 

The Mayo model can also be used to predict the 
functionality of the polymer obtained. If we multiply both 
sides of equation 4.4 by DP n/ we get 

DP,, — [S] 

where the two terms on the right represent the fraction of 
unfunctionalized and f unctionalized chains. 

Synthesis . Butyl acrylate : cysteine :AIBN mole ratios of 
1000:64:1, 1000:32:1, 1000:16:1, 1000:0:1, were polymerized 
in a THF/H 2 0/HC1 solvent system identical to that previously 
described in section 4.1.2. The only difference was in the 
purification. After isolation, the polymers were extracted 
with Ultrapure™ water in order to remove any traces of 
unreacted cysteine or AIBN. 

GPC results . Molar mass distributions are shown in 
Figure 4.11. The Mn systematically decreases as the 
relative concentration of chain transfer agent is increased. 
The Mn of the neat poly (butyl acrylate) was 65kg/mol with a 
polydispersity index is 3.0. The Mn at the highest 
concentration of cysteine was 1.3kg/mol. The 



79 



polydispersities of the reactions in which cysteine is 
present are all significantly lower, i.e., around 2.0. 

A Mayo plot of the GPC data is depicted in Figure 4.12 
Referring back to equation 4.4, we can plot the relative 
concentration of chain transfer agent to monomer, [S]/[M], 
versus the inverse of the number average degree on 
polymerization. After performing a regression on the data, 
the slope of the line is the chain transfer constant, Cs . 
The chain transfer constant 



Cs = K / kp (4.6) 



where k tr is the rate constant for chain transfer. A larger 
chain transfer constant indicates increasing termination by 
chain transfer and thus the effectiveness of the chain 
transfer agent in participating in the polymerization. The 
chain transfer constant calculated for the butyl 
acrylateicysteine system was 1.49. Reported Cs values for 
other mercaptans are generally between 0.8 and 1.2. As 
stated previously, we have studied mercaptoethanol as a 
chain transfer agent and found a Cs of 1.1. Thus, cysteine 
is an extremely effective chain transfer agent in the 
polymerization of poly (butyl acrylate). 

Spectroscopic characterization. FTIR was run in order 
to observe any differences in structure between the neat 
poly (butyl acrylate) and the product of the cysteine 



> 

E 



40 



30 



20 - 



10 




1000:64 BAxysteine 
1000:32 BAxysteine 
1000:16 BAxysteine 
neat PBA 



5 4 

log (MW) 



Figure 4.11 GPC results of polymerizations of butyl 
acrylate varying cysteine concentrations 



o 

X 

Q 



12 
10 

8 
6 
4 
2 




1/DP n = 1/DP n + Cs[S]/[M] 

Cs=1.49 

r 2 = 0.99 



T = 65° 
THF/H20/HCI 
[AIBN] = 0.2wt% 
S : Cysteine 



6 



[S]/[M]x10 : 



Figure 4.12 Mayo plot for chain transfer constant 

determination for cysteine :butyl acrylate 
system. 



82 



modified polymerizations. Spectroscopic determination and 
quantification of amino acid functional groups is 
complicated by the low end group concentration relative to 
P(BA) . 

The only difference in the FTIR spectra of the lowest 
molar mass poly(butyl acrylate) macromonomer (1.2kg/mol) and 
the neat poly(butyl acrylate) (Figure 4.13). The only 
significant difference between the two spectra was the low 
intensity broad absorption from 3400-2400cm _1 . This was 
attributed the carboxylic acid from the cysteine end group. 

NMR spectroscopy was used in an attempt to better prove 
the presence of the amino acid end-group. A comparison of 
the 1 H-NMR spectra of neat poly (butyl acrylate) (Fig 4.14) 
and the 1.2kg/mol macromonomer (Fig 4.15) reveals the 
presence of two very small, broad peaks around 8 2.8 and 3.3 
for the macromonomer. The chemical shift values are equal 
to the predicted shifts of the methylene and methine protons 
from the cysteine end-group (Sil91) . Again, the peaks are 
very low in intensity due to the low end group 
concentration. The 13 C-NMR spectra of the low molar mass 
macromonomer is shown in Figure 4.16. All peaks can be 
assigned to that of poly (butyl acrylate) with the exception 
of a small peak at 5 31.8 which is assigned to the C-S-R 
carbon . 

ICP was used to determine the sulfur concentration in 
the p(BA). As described in section 3.2.1, this value in 



83 



O 

c 
n 

-Q 
O 

< 



1.0 



0.8 



0.6 



0.4 



Poly(butyl acrylate) 



0.2 - 



Amino acid 

terminated 

P(BA) 



0.0 >- 



4000 




I ■ ■ ■ | < < • | ' ' I | I I I | I c I I i I ■ I • I • I I I ■ I I I I I I I I I ■ • I I I I I I I I I | 



3000 2000 

Wavenumbers (cm-1) 



1000 



Figure 4.13 FTIR spectra of poly (butyl acrylate) and 
cysteine end-capped p(BA) macromonomer . 
Macromonomer is the 1.2kg/mol p(BA) 
synthesized using 1000:64:1 butyl 
acrylate:cysteine : AIBN mole ratio. 



9 4 



f 

4ch 2 - 



e 

CH-)- 
x 



c=o 



O 

I 
CH 2 



CH 2 

I 
CH 2 

I 
CH 3 



c 

b 

a 



a 





TMS 



«UL 



1 I ' I I I < " 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 



1 PP m 



Figure 4.14 X H-NMR spectra of neat poly (butyl acrylate) . 



8 5 



OH 



0= ? g f e 

hCH-CH 2 -S-(-CH 2 -CH-)- 



NH- 



i — i — r 



X 

c— o 



o 

CHo d 



:h 2 c 



ch 2 b 



CH 



a 



TMS 



a 




1 



Kl. 



i i i | i i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — p — r 



PPm 



Figure 4.15 X H-NMR spectra of 1.2kg/mol cysteine modidied 
poly (butyl acrylate) . 



8 6 



OH 



o=c 



h , g f , 
CH-CH 2 -sfCH 2 -CHi- 

x 




180 160 140 120 100 80 60 40 20 ppm 



Figure 4.16 13 C-NMR spectra of 1.2kg/mol cysteine modidfied 
poly(butyl acrylate) . 



combination with the measured molar mass values allows us to 
estimate the percent f unctionalization (Table 4.2). 



TABLE 4.2 Percent functionalization versus molar mass for 
poly (butyl acrylate) macromonomers . 



[S/M] 

2 
x 10 


Mn 
(Kg/mole) 


% functionalization 
(ICP- S cone. ) 


Predicted % 
functionalization* 





63 








1.6 


5.9 


72 ± 2 


91 


3.2 


2.6 


75 ± 2 


96 


6.4 


1.3 


84 ± 1 


98 



Functionalization= l-DP n /Dp no derived from equation 4.5. [S/M] 
relative molar concentration of cysteine to butyl acrylate. 



As the concentration of cysteine was increased, the 
percent functionalization of chains increases up to 84% for 
the lowest molar mass sample. This trend of increasing 
functionalization with increasing cysteine concentration 
also held for the predicted functionalities from the Mayo 
model. This would imply that chain transfer dominates the 
termination process as the chain transfer agent 
concentration increases. Also, the probability of 
initiation by an AIBN radical versus a mercapto sulfur 
radical decreases. 

The differences in the predicted and experimental 
functionalities may be accounted for by experimental 



methodology used to measure these values. As stated 
previously in section 3.2.1, these values are calculated 
under the assumption that the molar masses measured by GPC 
are absolute, where in fact these values are relative to 
polystyrene standards. In other words, our measured molar 
mass is the molar mass of the polystyrene standard whose 
hydrodynamic volume is equal to our sample. Nonetheless, 
because of similar solubility parameters, monomer molar 
masses, and backbone chemistry for poly (styrene) and 
poly (butyl acrylate) , these estimates should be reasonably 
accurate. It must be noted that the values predicted by the 
Mayo model are also estimates calculated under the 
assumption of ideal conditions. 

It is reasonable to assume that the sulfur content 
measured by ICP for the macromonomer is present due to the 
cysteine end-group. If this is the case, then for every 
mole of sulfur we have a mole of amino acid. Therefore we 
are estimating that between 72 and 84% of all chains possess 
the amino acid functionality and therefore the ability 
participate in a condensation reaction. 

4 . 1.4 .Cysteine Chain Transfer in the Synthesis of Amino 

Acid-terminated Poly (methyl methacrylate : octaf luoropentyl 
methacrylate) Macromonomers 

Fluoroacrylate copolymers were also polymerized in the 
presence of cysteine in order to produce amino acid 
terminated f luoropolymers . Fluoropolymers are known for 



their low surface energy. They have been blended with more 
hydrophilic polymers to reduce their moisture absorption. 
If f luoropolymers could be synthesized which were capable of 
grafting into a polyamide backbone, we could envision this 
graft copolymer could be used as a potential surface 
modifier for polyamides. 

The f luoropolymer chosen in this study is 
octafluoropentyl methacrylate (OFPMA) . Because of concern 
over the solubility of a homopolymer of OFPMA in the graft 
copolymerization reaction, copolymers of this f luoroacrylate 
with methyl methacrylate (MMA) were synthesized. The 
copolymer structure is depicted in Figure 4.17. The MMA to 
OFPMA, monomer molar masses of 100 and 300g/mol 
respectively, were mixed in a 1:1 weight ratio to yield a 
mole ratio of 3 : 1 MMA: OFPMA. 

Monomer: cysteine :AIBN mole ratios of 1000:64:1, 
1000:32:1, 1000:0:1, were polymerized in a THF/H20/HC1 
solvent system. Polymerization conditions and solvent 
composition were identical to those in section 4.1.2. The 
only difference came in the isolation of the product. The 
copolymers, which were isolated by precipitation in a 5X 
excess of methanol, were filtered and dried overnight under 
vacuum at 40°C. A white precipitate was isolated and then 
ground into a powder. 

GPC results . Molar mass distributions of the three 
copolymers are shown in Figure 4.18 and the molar mass 
averages are tabulated in Table 4.3. Mn values decrease 



90 



Poly(methyl methacrylate-co-octafluoropentyl methacrylate) 

CH 3 CH 3 

-eCH 2 -CXCH 2 — C^- 

0.75 0.25 

c=o c=o 

I I 

o 

1 I 

CH 3 H— C-H 

I 
H— C— F 

I 
F— C— F 

I 
F— C— F 

I 
F— C— F 

I 

F 

Figure 4.17 Chemical structure of f luoroacrylate copolymer. 



91 



1000:64:1 monomer:cysteine:AIBN 
1000:32:1 monomer:cysteine:AIBN 
1000:0:1 monomer:cysteine:AIBN 



20 - 



mV 




6 5 

log (MW) 



4 



Figure 4.18 GPC result of chain transfer polymerizations of 
f luoroacrylate copolymers. 



TABLE 4.3 Molar mass values of f luoroacrylate copolymers 
from GPC. 



[M] : [S] : [AIBN] 


Mn 
(kg/mol) 


Mw 
(kg/mol) 


PDI 


1000: 64:1 


19.9 


34.3 


2.2 


1000:32:1 


27.1 


51.3 


2.1 


1000:0:1 


72.1 


204. 6 


2.8 


M= monomer, S= cysteine 


a 







92 



from 72kg/mol in the neat polymerization to 27 and 
19.9kg/mole in the presence of varying amounts of cysteine. 
The molar mass distributions also are narrower, with 
polydispersities going from 2.8 in the neat sample to 2.1 in 
the cysteine modified polymerizations. Although the 
presence of the cysteine chain transfer agent causes a 
decrease in molar mass, it does so to a much lower extent 
than in the previous butyl acrylate polymerizations. Figure 
4.19 shows a comparison of the effect of cysteine on the 
polymerizations of butyl acrylate and MMA-OFPMA. Both 
distributions shown are for the 1000:32:1 mole ratios of 
monomer : cysteine : AIBN . 

It is evident that rate of chain transfer in the 
f luoroacrylate polymerization is substantially lower than 
that in the butyl acrylate reaction. In order to quantify 
this decrease in chain transfer, the chain transfer constant 
for the cysteine: f luoroacrylate system must be determined. 

In order to generate a Mayo plot for this reaction, the 
degree of polymerization for the poly (MMA-OFPMA) must be 
calculated from the GPC data. But the actual composition of 
the copolymer, in terms of mole percent MMA and OFPMA, is 
not known and thus the average monomer molar mass and thus 
the degree of polymerization cannot be calculated. Due to 
possible differences in free radical reactivity ratios, the 
composition of the polymer is not expected to be equivalent 
the monomer feed composition. 



^ 



p(BA) 

1000:32 monomer:cysteine 
Mn=2.6kg/mol 
p(mma-co-ofpma) 
40 000: 32: monomer: cysteine 
Mn=27.1kg/mol 




log (MW) 



Figure 4.19 



Comparison of effectiveness of chain transfer 
for p(BA) and f luoroacrylate copolymer. 



44 



NMR spectroscopy was used to determine the comonomer 
distribution in the f luoroacrylate copolymer. The spectra 
for the copolymer is shown in Figure 4.20. The mole percent 
fluoroacrylate was calculated from the integral ratio of - 
OCH 2 - at ~ 8 4.4 4 from the OFPMA to the -OCH 3 protons at ~ 8 
3.60 for MMA. Although the feed mole ratio was 3:1 
MMA: OFPMA the copolymer composition was closer to 2 : 1 with 
68 mole % MMA. NMR was run on all three copolymers and no 
difference in copolymer composition was observed. 

Given the composition of the MMA-OFPMA copolymers, we 
can calculate an average monomer molar mass and thus the 
degree of polymerization of our copolymer series. This 
allows us to generate a Mayo plot, shown in Figure 4.21, for 
the copolymerization of MMA-OFPMA in the presence of 
cysteine. The chain transfer constant for this reaction has 
been calculated to be 0.26, significantly lower than the 
1.49 chain transfer constant for the butyl acrylate 
polymerization . 

The cause of the differences between the two may be due 
to the lower reactivity of methacrylates versus acrylates 
(Nai94) . Nair has reported that degradative chain transfer 
in less reactive monomers. That is, the rate of 
polymerization decreases with increasing concentration of 
mercaptans. Nair attributes this to the mutual destruction 
of sulfur radicals, by combination to form disulfides, and 
to slow reinitiation by the sulfur radical. 



4b 



c 7 

CH 3 



c 

CH 3 



d' d 

4ch 2 -c^-4ch 2 -c-4 

x y 

C=0 C=0 



O 



CH 



CH 2 D 

a HCF 

I 
CF 2 

CF 2 
CF 3 



a 



~| 1 1 1 1 1 1 1 1 1 1 1 1 1 r- - | " ~i 1 1 r 1 — 

7 6 5 4 3 



TMS 



C,C 




-| 1 1 1 1 1 . . . 1 r 

2 1 



Figure 4.20 ^-NMR spectra of MMA-OFPMA macro-monomer 



Mb 



Q 



1.0 

0.9- 
0.8- 
0.7- 
0.6- 
0.5- 
0.4^ 
0.3- 
0.2 



1/DP n =1/DP n +Cs[S]/[M] 
Cs = 0.26 
r 2 = 0.98 



[S]/[M]x10 



Figure 4.21 Mayo plot for chain transfer constant 

determination for cysteine :MMA-co-OFPMA system. 



97 



Conclusive evidence of the presence of the amino acid 
functionality on these copolymers was not observed in the 
NMR spectra of the lowest Mn copolymer (Figure 4.20) . Also, 
the FTIR spectra of the neat MMA-OFPMA copolymer and that 
polymerized at the highest cysteine concentration, shown in 
Figure 4.22, display no observable differences. 

It must be noted that because the molar mass values of 
the f luoroacrylate copolymers are substantially higher than 
the poly (butyl acrylate) macromonomers, the relative 
concentration of end groups is substantially lower and 
therefore more difficult to detect. Also, ICP could not be 
used to determine sulfur concentration because stable 
agueous emulsions could not be made. This could be due to 
both the hydrophobicity of the copolymer as well as the 
higher glass transition temperature compared to the p(BA). 
The only values of functionality available are those 
predicted by the Mayo model, 62 and 73% for the two MMA-co- 
OFPMA macromonomers . 

These values significantly lower than the predicted 
functionality of the p(BA) macromonomers from Table 4.2. 
Conclusive proof of functionality will be determined by the 
copolymers ability to react in a condensation grafting 
reaction . 



98 



1.0 



0.8 



<u 0.6 
o 

c 

03 

-Q 
i_ 
O 
C/) 

jQ 

< 0.4 



Neat Poly (MMA-OFPMA) 

1000:0:1 
monomer : cysteine : AIBN 




Poly (MMA-OFPMA) 
0.2 1 1000:64:1 

\ monomer : cysteine : AIBN 



0.0 




ft I • I I I • I • I I I ■ I I I I I I I ■ 1 ■ I I 1 I I t 1 I I I I I I I I I I ■ I I I I I 

4000 3000 2000 

Wavenumbers (cm-1) 




Figure 4.22 FTIR spectra of MMA-OFPMA copolymers 



99 



4.2. Poly (amide-g-acrylate) Graft Copolymers from Amino 
Acid-terminated Macromonomers 



Most of the macromonomers described in the literature 
contain unsaturated end-groups allowing for graft 
copolymerizations . Therefore, the majority of the studies 
involving the graft copolymerization of macromonomers have 
concentrated on the free radical graft polymerization of 
vinyl monomers. This study is focused on the condensation 
graft copolymerization of the previously synthesized 
poly (acrylate) and poly (methacrylate) macromonomers with 
polyamide precursors. 

4 . 2 . 1 . Synthesis of Poly (amide-g-butyl acrylate) 

A general reaction schematic is illustrated in Figure 
4.23. The amino acid functionality of the poly (butyl 
acrylate) reacts with the specified amino acid in a 
condensation reaction producing an amide-acrylate graft 
copolymer and water. 

The polyamide graft copolymer synthesis was carried out 
in a solvent system originally developed by Higashi (Hig80a, 
Hig80b, Hig80c) for the solution polymerization of high 
molar mass polyamides . This polymerization of diacids and 
diamines was run in an NMP-pyridine cosolvent mixture, in 
the presence of triphenyl phosphite (TPP) and LiCl . The 
pyridine aids in the dissolution of the amino acid 



100 



NH,- 



CH 2 

I 

S 







Polyamide 



-COOH + NH 2 -R— C— OH 




+ 



H,0 



P(BA) 



Poly (butyl aery late) 



Figure 4.23 Amide-acrylate graft copolymer structure 



101 



reactants. Triphenyl phosphite catalyzes the polymerization 
by reacting with the acids and amines to remove water from 
the condensation. LiCl facilitates the reaction of the 
triphenyl phosphite. 

The condensation mechanism, as proposed by Higashi, is 
illustrated in Figure 4.24. Triphenyl phosphite reacts with 
LiCl to form a triphenyl phosphonium salt (Step 1) . The 
phosphonium salt then reacts with a carboxylic acid to form 
a diphenyl phosphonium cation and a phenolic anion (Step 2) . 
An amine can then attack the carboxylic acid, producing an 
amide linkage, diphenyl phosphite, and phenol (Step 3) . 

Synthesis . The synthesized graft copolymer 
compositions are shown in Figure 4.25. Two different 
polyamide compositions, a wholly aromatic poly (aminobenzoic 
acid) (PABA) and an aromatic-aliphatic poly (phenylene 
diamine-co-adipic acid) (PhDAA) , were homopolymerized and 
graft copolymerized in varying ratios with a 2 . 6kg/mol amino 
acid-terminated poly (butyl acrylate) macromonomer . A 
control reaction was run in which a 3.2kg/mol 
unfunctionalized poly (butyl acrylate) was substituted for 
the low molar mass poly (butyl acrylate) macromonomer. This 
unfunctionalized p(BA) was synthesized using a butyl 
mercaptan chain transfer agent, which should result in an 
unreactive butyl end group. PhDAA was also polymerized in 
the presence of a 19.9kg/mol poly (MMA-co-OFPMA) 
macromonomer . 



102 





i CHH3 + — O-ghO 

^' Li 






\\ /f^ c f[^ ^ + RCO ° H 





\ // 



4-H <b-/"\ 

O ^^ 

R Li + Cl- 





\ // 






O 
R 



O 



+ R'NH2 



RC-NH-R' + HO— <f \ + 







OH 



Ah 



Figure 4.24 Triphenyl phosphite driven amide formation, 



103 



Polyamide 
precursors 



Macromonomer 
(type) (weight %) Sample ID 



9 
Ho-c-f Vnh 2 



NH- 



9 



o 



NH 2 HO-C-(CH 2 )4-C-OH 



PABA 



2.6 kg/mole 


33 


66PABA-g-33BA 


P(BA) 
2.6 kg/mole 


66 


33PABA-g-66BA 


OH — 





PhDAA 


p(BA) 

2.6 kg/mole 


66 


33PhDAA-g-66BA 


P(BA) 
2.6 kg/mole 


90 


10PhDAA-g-90BA 


p(MMA-co-OFPMA) 

19.9 kg/mole 


66 


33PhDAA-g-66FA 


p(BA)- nonfunctional ized 
3.2 kg/mole 


66 


33PhDAA-g-66UBA 



Figure 4.25 Synthesized graft copolymer compositions. 



104 



In a typical reaction, 1.37g of 2 . 6 kg/mol p(BA) 
macromonomer (0.53 mmol), 0.241g (2.24 mmol) p- 
phenylenediamine, 0.326g (2.24 mmol) adipic acid, 1.55g TPP 
(5mmol) , and 0.09g LiCl were dissolved in 30ml of an 80/20 
NMP/pyridine solution and heated at 100°C for 4 hours. The 
resulting polymer, a tacky light brown solid, was obtained 
almost quantitatively by precipitation in an excess of 50/50 
water/methanol nonsolvent, filtered, washed with methanol 
and dried overnight under vacuum at 40°C. The molar 
concentration of amide precursors and catalysts were kept 
constant for all polymerizations. 

The PABA containing polyamides were insoluble in all 
common organic solvents. Those tried included THF, DMF, 
dichloroacetic acid and trif luoroacetic acid. The only 
solvent found for both the PABA homopolymer and copolymer 
was concentrated sulfuric acid. This is not surprising 
given the similarity of the aromatic structure in PABA to 
Kevlar® polyamides. PhDAA homopolymer and copolymers were 
soluble in both dichloroacteic acid and concentrated 
sulfuric acid. 

4 .2 .2 .Characterization of Graft Copolymers 

Soxhlet extraction of graft copolymers . All polyamide 
homopolymers and graft copolymers were Soxhlet extracted 
with HPLC grade THF, an excellent solvent for any unreacted 
acrylate or methacrylate macromonomer. Grafted polyamides 



105 



displayed significant swelling in the THF solution. Weight 
loss during extraction is shown in Table 4.4. 



TABLE 4.4 Percent weight loss from Soxhlet extraction for 
polyamide graft copolymers. 



Polyamide Graft Copolymer 


% Weight loss 


PABA 


0.4 


66PABA-g-33BA 


not measured 


33PABA-g-66BA 


44 


PhDAA 


0.6 


33PhDAA-g-66BA 


42 


10PhDAA-g-90BA 


80 


33PhDAA-g-66FA 


58 


33PhDAA-g-66UBA 


68 



The polyamide homopolymers display negligible weight 
loss during extraction whereas the graft copolymers lost 
between 44 and 80 weight % during extraction. 33PhDAA-g-66FA 
shows a much higher weight loss than the corresponding p(BA) 
graft copolymers. This could be attributed to the 
unfunctionalized chains due to the lower chain transfer 
constant and thus lower efficiency of functionalization in 
the polymerization of the f luoroacrylate macromonomer . In 
the control polymerization, the weight loss almost 
guantitatively matches the amount of unfunctionalized p(BA) 
added to the reaction. This would indicate that the 
unfunctionalized p(BA) is not capable of reacting with the 



106 



amide precursors in a graft copolymerization . Therefore, 
any incorporation of the p(BA) macromonomers can be 
attributed to amino acid functionality. 

Due to the significant weight loss during extraction of 
the macromonomer-graf ted polyamides, it would initially 
appear that a large fraction of macromonomers are 
unfunctionalized and therefore cannot participate in the 
condensation polymerization. GPC was run on the extracted 
solutions and FTIR spectra collected of the pre and post- 
extracted graft polyamides in to order better explain the 
Soxhlet results. 

GPC results . Figure 4.26 shows comparison of the molar 
mass distributions (from the refractive index detector) of 
the extracted fraction of the 33PABA-g-66PBA graft copolymer 
and the original p(BA) macromonomer . The extracted fraction 
is not purely unreacted macromonomer. The distribution is 
bimodal, with a high molar mass component at approximately 
lOOkg/mol and a low molar mass fraction near the original 
macromonomer molar mass. 

The GPC data was also collected using a photodiode 
array detector measuring UV absorption. The UV spectra from 
200-400nm for the high and low molar mass components in the 
extracted solution can be seen in Figure 4.27. The spectra 
can be compared with that of the original macromonomer. 
P(BA) shows a single absorbance centered around 220nm 
characteristic of the n -» n* transitions of carbonyl 
containing compounds (Sil91) . 



107 



> 

E 



70 
60 
50 



p(BA) macromonomer 
33PABA-g-66BA 



5 4 

logMW 




Figure 4.26 Molar mass distributions of dissolved polymer 
in THF extractant solution of 33PABA-g-66BA 
(refractive index detector) . 



108 




13 
< 



33PABA-g-66BA 
(high mw traction) 




33PABA-g-66BA 
(low mw fraction) 




Poly(butyl acrylate) 
Macromonomer 



200 



300 
nm 



400 



Figure 4.27 UV spectra of dissolved polymer in THF 

extractant solution of 33PABA-g-66BA from GPC- 
UV. 



109 



Both the high and low molar mass components in the 
extractant solution contain two absorbances, one around 
220nm and the other centered at 315nm. This second 
absorption can be assigned to the n — > n* transition typical 
of conjugated aromatic compounds. 

This transition is indicative of the presence of 
aromatic polyamide segments. In other words, neither of the 
components in the extractant solution can be attributed to 
purely unreacted poly (butyl acrylate) macromonomer . The 
high molar mass component can therefore be interpreted as 
amide-acrylate graft copolymer. This may be attributed 
either to limited solubility of our unextracted product in 
THF or to a higher local distribution of poly (butyl 
acrylate) in this fraction which determines its solubility. 

The presence of aromatic UV absorption in the low molar 
mass component, with an average molar mass similar to that 
of the original macromonomer, is more difficult to 
interpret. It is believed that this fraction is a mixture 
of unreacted p(BA) macromonomer, due to unf unctionalized 
chains, as well as very low molar mass graft copolymer in 
which the amino acid terminated macromonomer has reacted 
with only a few monomer units of p-aminobenzoic acid. 

Similar results were obtained for the aromatic- 
aliphatic PhDAA graft copolymers. Figure 4.28 shows 
comparison of the molar mass distribution of the extracted 
fraction of the 33PhDAA-g-66PBA graft copolymer and the 
original p(BA) macromonomer. The extracted fraction again 



110 



100 



> 

E 



p(BA) macromonomer 
33PhDAA-g-66BA 



r\ _< t i r - * r r - * l"/''Tl'"jlf'' 




5 4 

logMW 



Figure 4.28 Molar mass distributions of dissolved polymer 
in THF extractant solution of 33PhDAA-g-66BA 
(refractive index detector) . 



Ill 



is bimodal. The high molar mass component has a larger 
molar mass, around 160kg/mol, than that in the PABA graft 
copolymer. This peak is also more intense than in the 
previous case. This may be due to the structure of the 
polyamide. Copolymers with PhDAA, an aliphatic-aromatic 
amide, should be more soluble than the wholly aromatic PABA. 

The UV spectra of the 160 and 6kg/mol components in the 
extracted solution can be seen in Figure 4.29. Each 
component shows two distinct regions of absorbance, with the 
longer wavelength absorbance centered around 270nm 
attributed to the n -> n* transition from the phenylene 
diamine units of the copolymer. The lower wavelength of the 
7i -> 7i* transition in comparison to the PABA copolymers (270 
vs. 315nm) is due to the difference in electronic structure 
caused by the variations in aromatic substitution. 

The higher molar mass component of the extraction 
displays a more intense aromatic absorption than the 6kg/mol 
component, indicative of a higher concentration of polyamide 
in the graft copolymer. Similarly to the PABA copolymer, it 
is believed that the 6kg/mol fraction is a mixture of 
unreacted p(BA) macromonomer, due to unf unctionalized 
chains, as well as very low molar mass graft copolymer in 
which the amino acid terminated macromonomer has reacted 
with only a few monomer units of phenylenediamine and adipic 
acid. 

The results from GPC analysis (Figure 4.30) and UV 
spectroscopy (Figure 4.31) of the 10PhDAA-g-90BA 



112 




< 



200 



33PhDAA-g-66PBA 
(high mw fraction) 




33PhDAA- g- 66PBA 
(low mw fraction) 




Poly(butyl acrylate) 
Macromonomer 



400 



Figure 4.29 UV spectra of dissolved polymer in THF 

extractant solution of 33PhDAA-g-66BA from 
GPC-UV. 



113 



p(BA) macromonomer 
10PhDAA-g-90BA 



20 - 



mV 



o - 



160K 




' " v -„,,/ 



log(MW) 



Figure 4.30 Molar mass distributions of dissolved polymer 
in THF extractant solution of 10PhDAA-g-90BA 
(refractive index detector) . 



114 



< 




200 



AA-g-90PBA 
mw fraction) 




10PhDAA-g-90PBA 
(low mw fraction) 




Poly(butyl acrylate) 
Macromonomer 



400 



Figure 4.31 UV spectra of dissolved polymer in THF 

extractant solution of 10PhDAA-g-90BA from 
GPC-UV. 



115 



are similar to the other graft copolymers. Only notable 
differences between this sample and the 33PhDAA-g-66BA will 
be discussed. This sample contains a higher relative 
concentration of high molar mass component than the 33PhDAA- 
g-66BA. With a higher poly (butyl acrylate) feed 
composition, the resulting copolymer should be higher in 
p(BA) thus making it more soluble in THF. This would help 
to explain the increase in intensity of the high molar mass 
peak as well as the large % weight loss during extraction, 
80%, as compared to lower acrylate containing compositions. 
The UV spectra follows similar trends with respect to the 
previously described graft copolymers. 

The molar mass distributions and UV spectra of the 
33PhDAA-g-66FA extractables are shown in Figures 4.32 and 
4.33 respectively. The extracted fraction is again bimodal 
with a high molar mass component around 270kg/mol. The 
relative concentration of high to low molar mass components 
was the highest of all graft copolymerizations . The 
starting macromonomer molar mass for the f luoroacrylate 
copolymer, 19.9kg/mol vs. 2 . 6kg/mol for the poly (butyl 
acrylate) graft reactions, may account for the difference in 
molar mass and intensity of the high molar mass fraction. 

The UV results are similar to those of the previously 
described graft copolymers. The most significant difference 
is the reduced intensity of the 71 -> n* transition for the 
low molar mass fraction. This is due to the high molar mass 
of the macromonomer. This higher molar mass macromonomer, 



116 



p(FA) macromonomer 
33PhDAA-g-66FA 



10 

mV 







»'. 



i ■ » r . «, >«> .» j »*C* * * * a • * 




5 



4 



logMW 



Figure 4.32 Molar mass distributions of dissolved polymer 
in THF extractant solution of 33PhDAA-g-66FA 
(refractive index detector) . 



117 




< 



33PhdDAA-g-66FA 
(high mw fraction) 




33PhdDAA-g-66FA 
(low mw fraction) 




FA macromonomer 
(19.9kg/mol) 



200 



300 

nm 



400 



Figure 4.33 UV spectra of dissolved polymer in THF 

extractant solution of 33PhDAA-g-66FA from 
GPC-UV. 



118 



caused by less effective chain transfer in the f luoropolymer 
polymerization, should contain a larger concentration of 
unfunctionalized chains. 

As was mentioned previously, a control polymerization, 
in which PhDAA is polymerized in the presence of an 
unfunctionalized low molar mass poly (butyl acrylate), was 
run under identical conditions to other grafting reactions 
(Sample 33PhDAA-g-66UBA) . The molar mass distributions 
(Figures 4.34) of the extractant from this reaction and the 
unfunctionalized p(BA) are nearly identical. There is also 
no difference in the UV spectra (Figure 4.35) of the two 
polymers. As was stated previously, the percent weight loss 
during extraction was almost identical to the initial feed 
concentration of p(BA). Hence, the extracted fraction was 
exclusively unreacted poly (butyl acrylate). In other words, 
grafting occurs only when the poly (butyl acrylate) is amino 
acid- terminated. 

FTIR results . FTIR spectra was collected in order to 
verify the presence of both the polyamide and acrylate 
segments, and to monitor the change in structure before and 
after extraction. Sample designation will contain an 'x' 
signifying that the polymer has been purified by extraction. 
For instance, 33PABA-g-66BAx designates the graft copolymer 
that has been purified by extraction and 33PABA-g-66BA 
identifies the neat polymer recovered directly from the 
graft copolymerization by precipitation. 



119 





Functionalized p(BA) 
PhDAA-g-66UBA 


\ 
\ 

\ \ 

\ ^. 
\ \ 

I k 
\ V 

\ \ 

\ \ 

\ s 

V\ '*» 

\v *' 
\ V ' • 

\ * 

\ V 

\ % 


uni 
331 


80 - 

mV 

o - 


rj 
A 

// 
// 
// 

1 1 1 




■'» 

1 L 



log(MW) 



Figure 4.34 Molar mass distributions of dissolved polymer 
in THF extractant solution of 33PhDAA-g-66UBA 
(refractive index detector) . 



120 




< 



33PhDAA-g-66UBA 



unfunctionalized p(BA) 




200 



300 
nm 



400 



Figure 4 . 35 



UV spectra of dissolved polymer in THF 
extractant solution of 33PhDAA-g-66UBA from 
GPC-UV. 



121 



In Figure 4.36, the spectrum of 66PABA-g-33BAx is 
compared to that of the macromonomer and the PABA 
homopolyamide . Absorbances typical of aromatic polyamides, 
the N-H stretch at 3300cm" 1 , the C=0 amide stretch at 
1658cm" 1 , and an overlap of the N-H bend and C=C stretch 
around 1513cm" 1 , are observed for the poly (p-aminobenzoic 
acid) (PABA) . 

The p(BA) macromonomer displays distinct aliphatic C-H 
stretch absorptions centered at 2965cm" 1 as well as the 
characteristic C=0 stretch for the ester carbonyl at 
1732cm" 1 . The purified graft copolymer 66PABA-g-33BAx 
display absorptions characteristic of both the poly (butyl 
acrylate) and the aromatic polyamide segments in the graft 
copolymer. Actual fractions of each phase will not be 
calculated using FTIR. Nitrogen content from elemental 
analysis was used to determine the actual polyamide content 
in the graft copolymers and these results will be discussed 
later. It must be noted that the spectra of the unpurified 
neat 66PABA-g-33BA is not shown because the entire sample 
was purified by extraction. However, the spectra of both 
the purified and unpurified graft copolymers will be 
displayed for all of the other compositions. 

Figure 4.37 shows the FTIR spectra of 33PABA-g-66BA 
before and after extraction. As expected the poly (butyl 
acrylate) absorptions are more intense than for the previous 
sample containing only 33% poly (butyl acrylate) in the feed. 
Also, there is a visible decrease in the ester carbonyl 



122 



: poly(p-aminobenzoic acid) 



0.8 - 



1513 




a) 0.6 
o 

c 

03 
JQ 

i— 

o 
tf) 



< 0.4 4 



\ p(BA) macromonomer 



2965 




] 66PABA-g-33BAx 

0.2 \ 3300 



0.0 :- 
4000 



1732 




1513 




3000 2000 

Wavenumbers (cm-1) 



Figure 4.36 Transmission FTIR spectra of 66PABA-g-33BAx 
graft copolymer. 



123 



1.0 



0.8^ 



PABA 



0.6 



• 33PABA-g-66BA 



0.4 



33PABA-g-66BAx 



0.2 



0.0 



1658 



1513 




1732 






7 i i i | i i i | i i i | i i i | i i i | i i i | i i i | i i i | i i i | i i i | i i i | . i i ( i i i | i i i 1 1 1 1 | 1 1 i | it i-j-t-t t-| 



4000 



3000 2000 

Vtevenumbers (cm-1) 



1000 



Figure 4.37 Transmission FTIR spectra of 33PABA-g-66BAx 
graft copolymer. 



124 



intensity after extraction with THF. This would indicate 
that the majority of polymer extracted is either unreacted 
poly (butyl acrylate) or high volume fraction poly (butyl 
acrylate) -containing graft copolymer. 

The spectra of PhDAA is very similar to that of PABA, 
with characteristic amide absorbances at the expected 
wavelengths (Fig 4.38). The major difference between the 
PABA and PhDAA is the presence of an aliphatic C-H stretch 
region around 2945cm" 1 from the methylene group in the 
adipic acid segments. The spectra of 33PhDAA-g-66PBA and 
33PhDAA-g-66PBAx both indicate the presence of p(BA) by the 
1732cm" 1 ester carbonyl stretch. 

Referring back to Table 4.4, this sample showed a 42% 
weight loss during extraction. Again, there is a visible 
decrease in the ester carbonyl intensity after extraction 
with THF indicating that the majority of polymer extracted 
was either unreacted poly (butyl acrylate) or high volume 
fraction poly (butyl acrylate) -containing graft copolymer. 

The FTIR analysis of the highest poly (butyl acrylate) - 
containing graft copolymer, 10PhDAA-g-90BA, (Figure 4.39) 
contains the spectra of the neat graft copolymer, the 
extracted graft copolymer and the THF soluble extrated 
fraction. The 10PhDAA-g-90BA displays the expected spectra, 
with a less intense amide carbonyl absorption (1658cm" 1 ) due 
to the decrease of amide precursors in the feed. The 
purified graft copolymer shows a decrease in poly (butyl 



125 



10 1 PhDAA 



0.8 




0.6 



i 33PhDAA-g-66BA 



</> 



33PhDAA-g-66BAx 



0.4 



0.2- 



0.0 

i • < • i 

4000 



1732 




1732 




| I I i | i i I | i I ■ | i I I | i . I | ■ I I | . i ■ | ■ . ■ | I ■ ■ | ■ i i | ■ • • | t-ri f I n | 



3000 2000 

Wavenumbers (cm-1) 



1000 



Figure 4.38 Transmission FTIR spectra of 33PhDAA-g-66BAx 
graft copolymer. 



126 



1.0 



0.8 



8 

c 
n 

| 

o 



0.6 



i 



0.0 




i lOPhDAA-g 
0.4 i -90BAx 



0.2- 



4000 



i i i i i i i i i i i 
3000 2000 

Wavenumbers (cm-1) 



1000 



Figure 4.39 Transmission FTIR spectra of 10PhDAA-g-90BAx 
graft copolymer. 



127 



acrylate) absorption, but still has the highest content of 
p(BA) of all of the graft copolymers. 

This can be seen in Figure 4.40, where the spectra of 
all of the purified poly (butyl acrylate) graft copolymers 
are displayed. As the butyl acrylate feed concentration is 
increased, there is an increase in the intensity of the 
ester carbonyl absorption (1732cm -1 ) relative to the amide 
carbonyl and N-H stretch. 

The last spectrum in Figure 4.39 is that of the THF 
soluble fraction of 10PhDAA-g-90BAx . Going back to Table 
4.4, 80 wt.% of 10PhDAA-g-90BA was extractable with THF. 
This THF solution was evaporated onto a NaCl crystal for 
FTIR analysis. The presence of the 1658cm" 1 amide, albeit 
small, correlates with the GPC-UV results that revealed the 
presence of polyamide graft copolymer within the THF 
extractable fraction. 

The FTIR spectra of the FA macromonomer , as illustrated 
in Figure 4.41, shows intense absorptions at 1732cm" 1 for 
the ester C=0 stretch and at 1170cm" 1 , which is an overlap 
of the C-0 stretch of the ester and the C-F stretch 
characteristic of f luoroalkanes . The spectra of the graft 
copolymer, 33PhDAA-g-66FA, confirms the incorporation of the 
FA macromonomers during the graft copolymerization . But the 
fluoroacrylate carbonyl absorption decreases in intensity by 
more than 50% after THF extraction. 

This decrease was much less significant in the spectra 
of the 33PABA-g-66BA and 33PhDAA-g-66BA graft copolymers. 



128 




Wavenumbers (cm-1) 



Figure 4.40 Transmission FTIR spectra of poly (butyl 
acrylate) grafted polyamides . 



129 



1.0" 



PhDAA 



1658, 



8 

c 

I 



to 



§ 0.4 




i i i i i i i i 
3000 2000 

Wavenumbers (cm-1) 



Figure 4.41 Transmission FTIR spectra of 10PhDAA-g-90BAx 
graft copolymer. 



130 



This confirmed the result from Table 4.4 in which the 
FA graft copolymer shows approximately 15% higher weight 
loss during extraction than the equivalent BA graft 
copolymers. This behavior can be explained by the higher Cs 
in the butyl acrylate macromonomer synthesis. A higher Cs 
leads to lower molar mass and more highly functionalized 
macromonomers which are more readily incorporated in the 
condensation grafting reaction. 

NMR and elemental analysis results . The compositions 
of the purified graft copolymers were determined by 
elemental analysis (EA) using from the nitrogen content. 
Composition was also determined from the """H-NMR spectra, 
shown in Figures 4.42 through 4.47, of the graft copolymers 
using the integral ratios of aromatic protons from the 
polyamide to methyl protons from the poly (acrylate) . 

The measured graft copolymer chemical compositions are 
tabulated in Table 4.5. The values calculated using NMR are 
in good agreement with those from EA. Poly (butyl acrylate) 
content varies from 19 to 54 wt . % for the graft copolymer 
series. As expected, the poly (butyl acrylate) content in the 
graft copolymer increases with increasing feed 
concentration . 

The ratio of poly (acrylate) concentration in the 
copolymer to the initial feed concentration was calculated 
and is also shown in Table 4.5. This ratio can be seen as a 



131 



b c c b 



f-C-CH ? CH 2 -CH 2 .CH 2 -C— NH 



H 2 S0 4 




a 



J 



c,c 



b,b' 



n Uww>ywM* fi^**» 




i i i | i i i i | i i ii [ i i i i | i i i i | i i i i | i i i i | i i ii I i i i i | i i i i I i i i i | i i i i | i i i 

11 10 9 8 7 6 5 4 3 2 1 ppm 



Figure 4.42 ^-NMR spectra of PhDAA homopolyamide . 



132 



f 



o 



-f-C-CH?Cht-CH2CH 2 -C— NH 

*' r J I 9 



H 2 S0 4 




O 



Nh+)— (-C-CH2-NH+); 



g 



■ w j 



S< » i »w M H aj M^i 



CH2 



CH2 f 



CH3-CH2CH2-CH2-0 — C-CH e 
abed vU 




N i Mai * i» 



I I | M I I | I I I I | I I I I | I | I I | M I I | I I II | I I I I | I I I I | I I I I | I I I I | I I I I I I I I 

1110 987 65 4 32 10 ppm 



Figure 4.43 ^-NMR spectra of 33PhDAA-g-66BAx 



133 



h H H h 



O O \ / O 

-(-C-CH2CH2-CH2CH2-C-NH— f ^ NH-)— fc-CH 2 -NH-)- 



;j ;> 



1 J J 1 



H 2 S0 4 



J 




CH2 



h H H h 



I 



CH 2 f 



CH3-ChbCH2CH20— C-CH e 
abed \L/ a 



^' ' ' '1 nrii J i- -im*~ 




' I I I I I I I II I I P I II I I I I I I I I I I J I I I I I I I I l| I II I I I I I I I I 1 l| MM |l I I 

11 10 9 8 7 6 5 4 3 2 1 ppm 



Figure 4.44 ^-NMR spectra of 10PhDAA-90BAx. 



134 



O O \ ( o 



-f-C-CH 2 -CH 2 -CH 2 .CH 2 -C— NH 
g' h' h g 




NH-)— (-C-CH 2 -NH-)- 

x y 

CH 2 



n i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i [ i i i i | i i i 
11 10 9 8 7 6 5 4 3 2 1 ppm 



Figure 4.45 1 H-NMR spectra of 33PhDAA-66FAx , 



135 



H 2 S0 4 




r^% 




o 
nh4— (-c-ch 2 -nh4- 

CH 2 

S 
CH, f 



CH o'CH p'CHp'CHp'O — C — CH g 

abed 4^ 

zT 




i ' ' ' ' i ' ' ' ' i ' ' ' ' i 



11 10 987 65 4 3 210 ppm 



Figure 4.46 ^-NMR spectra of 66PABA-33BAx, 



136 




H 2 S0 4 



J 




o 



y J NH^-fC-CH 2 -NH^- 



CH 2 

S 
CH 2 f 



CH 3 -CH 2 -CH 2 CH 2 — C-CH e 

abed 4^ 

O zT 




1 I I I Ml | I I I I | I I I I | I I I I | I I I I | | | | | | M | | | | | | | | | | | | | | | | | | | | | | | | | | | 

11 10 9 8 7 6 5 4 3 2 1 ppm 

Figure 4.47 X H-NMR spectra of 33PABA-66BAx . 



137 



TABLE 4.5 Chemical composition of purified graft copolymers 
from elemental analysis and NMR. 



Sample ID 


Nitrogen 


Graft Copolymer 


Graft Copolymer 


[Acrylate] copolymer** 




(wt. %) EA 


Compos ition EA 
(wt. %)* 

Amide Acrylate 


Composition™" 
(wt. %) 

Amide Acrylate 


[Acrylate] feed 


66PABA-g-33BAx 


9.47 


81 19 


79 21 


0.61 


33PABA-g-66BAx 


6.35 


54 46 


60 40 


0.65 


33PhDAA-g-66BAx 


7.03 


55 45 


54 46 


0.69 


10PhDAA-g-90BAx 


6.42 


46 54 


47 53 


0.60 


33PhDAA-g-66FAx 


9.64 


75 25 


75 25 


0.38 



Calculated using wt %N for PABA=11.76, PhDAA=12.84. 
** based upon average of EA and NMR acrylate wt . %. 



measure of % poly (acrylate) incorporation. The values for 
the poly (butyl acrylate) containing graft copolymers, 
between 0.60 to 0.69, do not vary greatly. In other words 
the p(BA) content in the purified graft copolymers is 
approximately 60 to 69% of that in the feed. The result for 
the fluoroacrylate graft copolymer differs significantly 
with a copolymer to feed ratio of 0.38. This decrease in 
macromonomer incorporation can again be attributed to the 
decrease in macromonomer functionality from inefficient 
chain transfer for the fluoroacrylate polymerization. 

Inherent viscosities of graft copolymers . The 
intrinsic viscosities of the polyamide graft copolymers were 
measured in concentrated sulfuric acid at a concentration of 
0.005g/ml. The results are shown in Table 4.6. 



138 



TABLE 4.6 Inherent viscosities of polyamide graft 
copolymers . 



Sample ID 


Graft Copolymer 
Composition* 
(wt %) 

Amide Acrylate 


Tlinh** 


PABA 


100 


1.16 


66PABA-g-33BAx 


80 20 


0.88 


33PABA-g-66BAx 


57 43 


0.55 


PhDAA 


100 


1.24 


33PhDAA-g-66BAx 


55 45 


0.52 


10PhDAA-g-90BAx 


47 53 


0.37 


33PhDAA-g-66FAa 


75 25 


1.11 



♦average of EA and NMR results 

**measured in cone. H 2 S0 4 at 30°C, 0.005g/ml 



The Tjinh values of the PABA and PhDAA homopolyamides are 
1.16 and 1.24 respectively. The viscosity decreases as the 
poly (butyl acrylate) content in the graft copolymer 
increases. This decrease in viscosity is not as dramatic 
for the 25% FA grafted polyamide whose r|i n h is similar to 
that of the PhDAA homopolyamide, 1.11 vs. 1.24 respectively. 
By comparison, only 20% BA causes a decrease in the r|i nh of 
PABA from 1.16 to 0.88. 

These viscosity values can be used as an indication of 
the molar masses of the graft copolyamides . Quantitative 
molar mass values cannot be derived since the precise 
relationship between molar mass and viscosity is not known 
for these copolymers. However, it has been shown in the 



139 



copolymerization of other amino acids (Hig80b) that the 
viscosities determined for polyamides synthesized in 
Higashi's solvent system translate into molar mass values of 
approximately 15 to 35kg/mol. 

4. 2. 3 .Blends of Graft Copolymers with Nylon 6 

Preliminary experiments were performed in order to 
study the effect of graft copolymer addition on the 
mechanical properties of Nylon 6. BA-containing graft 
copolymers were blended with Nylon 6. Graft copolymers were 
also added to Nylon 6/Poly (butyl acrylate) incompatible 
blends in order to investigate the ability of the graft 
copolymer to act as a surfactant or compatibilizer . 

The synthesized copolymers, PhDAA, 33PhDAA-g-66BAx, and 
10PhDAA-g-90BAx were blended with Nylon 6. Also, 33PhDAA-g- 
66BAx and 10PhDAA-g-90BAx were added to an 85/15 blend of 
Nylon 6 and 65kg/mol poly (butyl acrylate). Blend and sample 
preparation has been described previously (section 3.2.2). 
Tensile properties of all blends can be found in Table 4.7. 



140 



TABLE 4.7 Tensile properties of nylon 6 blends 



Material 



Modulus 
(GPa) 



Proportional Limit 



Stress 
(MPa) 



Elongation 
(%) 



Stress at 

Failure 

(MPa) 



Elongation @ 

Failure 
(%) 



Nylon 6 

90 N6/10 
PhDAAx 

85 N6/15 

33PhDAA-g- 

66BAx 

85 N6/15 

lOPhDAA-g- 

90BAx 



1.60± 0.07 16.2+2.0 1.0± 0.2 

2.85+0.46 27.4+4.6 0.98+0.08 

1.02+0.03 9.95+1.03 1.0+0.1 

0.91+ 0.09 10.81+ 1.03 1.0+ 0.2 



90 N6/10 PBA 1.32+0.21 15.0+1.6 1.2+0.3 

90 N6/10 PBA 1.32+ 0.05 19.2+ 2.4 1.3+ 0.1 
w/0.6 wt% 
33PhDAA-g- 
RA66x 

90 N6/10 PBA 1.38+0.05 18.2+1.5 1.5+0.2 
w/0.6 wt% 
lOPhDAA-g- 
90BAx 



71.6+ 5.1 
83.0+ 7.3 

28.0+ 3.0 

24.4+ 4.1 

79.8+ 9.8 
63.9+ 4.5 

68.0+ 7.2 



55+9 
8.0+ 1.1 

7.2+ 1.9 

8.4+ 1.9 

50+ 29 
22+8 

20+ 14 



Addition of PhDAA to Nylon 6 produced an increase in 
modulus and a severe decrease in ductility. The modulus 
increased from 1.60 to 2.84 GPa with the addition of 10% 
PhDAA but the percent elongation at failure decreased from 
55 to 8%. The proportional stress increased from 16.2 to 
27.4 MPa upon PhDAA addition. The aromatic polyamide 
domains behave like hard inclusions within the nylon matrix, 
reinforcing nylon and serving as sites for stress 
concentration. This behavior is partly due to the visibly 
poor mixing between the nylon and the aromatic polyamide or 
graft copolymer. Dispersion is poor as off-colored regions 
of brown PhDAA are clearly visible. 



141 



Poor mixing is a result of the lack of thermal 
transitions for the amide phase not allowing flow during 
compression molding. The TG/DTA (Figure 4.48) and DSC 
(Figure 4.49) traces of the 33PhDAA-g-66BA graft copolymer 
and PhDAA display no thermal transitions prior to 
degradation for the amide phase. The only thermal 
transition observed is the glass transition of p(BA) . 
Yoshimitsu (Yos94) has reported that similar aromatic 
polyamides degrade before their melt temperature. 

As expected, the graft copolymer blend with Nylon 6 
also exhibits poor mixing due to the lack of mobility or 
flow during compression molding. Regions of graft copolymer 
are clearly visible within the nylon 6 film. However, the 
modulus, proportional stress , stress at break, and 
elongation at break of the blend containing 15% graft 
copolymer are significantly lower than that of the either 
the neat nylon 6 and the PhDAA/Nylon 6 blend. The large 
domains of graft copolymer do not reinforce the blend due to 
the presence of the rubbery p(BA) segments. In essence, we 
have gone from a system with hard inclusions to one with 
soft inclusions. These inclusions are very poorly dispersed 
and thus no toughening of the system is observed. 

The differences between the mechanical properties of 
the 85/15 blends of nylon 6/33PhDaa-g-66BAx and nylon 
6/10PhDAA-g-90BAx are not significant. The final 
compositions of the graft copolymers are not as dissimilar 
as their feed compositions. From Table 4.5, we have already 



142 






r 
o 



Figure 4.41 



33PhDAA-g-66BA 



PhDAA 




r- 180 
160 
140 
120 

- 100 

- 80 



- 20 

- 



175 350 525 700 

Temperature (°C) 



i 

825 



TG/DTA analysis of 33PhDAA-g-66BAx graft 
copolymer and PhDAA homopolyamide . 



> 






- 40 



143 



1000 

500 - 

- 

-500 - 

-1000 

-1500 

-2000 H 

-2500 



t 

-45°C 
P(BA) Tg 



PhDAA 



\ 



33PhDAA-g-66BA 







100 200 

Temperature (°C) 



300 



Figure 4.49 DSC analysis of 33PhDAA-g-66BAx graft copolymer 
and PhDAA homopolyamide . 



144 



shown that these two graft copolymers contain 45 and 55% BA 
respectively. 

The graft copolymer had little effect as a surfactant 
in the Nylon 6/poly (butyl acrylate) blend. Again, lack of 
mixing would prevent the graft copolymers from migrating to 
the interface between the immiscible polymers. Also, the 
poly (butyl acrylate) homopolymer migrated to the surface of 
the blend and thus the mechanical properties of these blends 
may not be representative of a 10% p(BA) content. The films 
had to be wiped with acetone prior to tensile testing in 
order to avoid slippage. 



4.3. Offsetting Polymerization Shrinkage in Dental Resins 
through the Incorporation of Maleic Anhydride 



Volumetric shrinkage is a major problem inhibiting the 
long term success of current dental restorative materials 
(Bau82). This shrinkage is inherent to the free radical 
polymerization of the multifunctional methacrylate resins 
used in the dental composites. The volumetric shrinkage is 
due to the reduction in molar volume, or spacing between 
monomer units, that occurs when vinyl compounds are 
polymerized. Polymerization shrinkage creates both a weak 
interface between the tooth structure and the restoration as 
well as residual stresses within the composite structure, 
leading to premature failure in the restoration (Bra86) . 

BisGMA is the predominant monomer currently in use in 
dental composites. Although the shrinkage is decreased from 



145 



that of simple methacrylates, BisGMA based composites still 
exhibit volumetric shrinkage values of around 3% (Sul93) . 
There have been some modifications to BisGMA. However, the 
differences are not generally significant and many 
manufacturers still rely on the BisGMA monomer for their 
dental composites. 

There are many research programs focused on different 
chemical structures and processes that will reduce 
polymerization shrinkage (Bra92, Bye92, Sta91). The main 
thrust in dentistry has been the spiro orthocarbonate based 
systems which are the result of early pioneering work by 
Bailey (Bai72). The spiro orthocarbonates involve a dual 
ring opening mechanism which increases the molar volume of 
the polymer compared to that of the monomer. The deficiency 
with these ring opening systems is the cost of the reactive 
monomer and the slow kinetics. Typically dental restorations 
can be cured within a few minutes whereas the spiro 
orthocarbonates are very slow reacting (Bra92, Bye92) . 

Although not ideal, these systems do provide some 
insight as to a logical step in the evolution of dental 
restoratives. The ring opening polymerization kinetics may 
be too slow, yet the ring opening mechanism does provide a 
net increase in molar volume. Thus, by combining the fast 
kinetics of the methacrylate resin with the ring opening 
reactions, one may reduce the polymerization shrinkage. 

The focus of our work is to incorporate cyclic 
anhydride functionality into dimethacrylate networks. When 



146 



maleic anhydride (MA) is ring opened by hydrolysis to maleic 
acid there is a corresponding theoretical 10% increase in 
molar volume. By incorporating maleic anhydride into common 
dental resins, such as a BisGMA/TEGDMA system, and then 
hydrolyzing the anhydride, we should offset some of the 
shrinkage associated with polymerization. 

4 . 3 . 1 . Copolymer Compositions 

A design study including the composition matrix shown 
in Table 4.8 was carried out. The composition ranges are 50- 
70 wt . % triethyleneglycol dimethacrylate, 20-40% 
propoxylated BisGMA (pBisGMA) , and 0-20% maleic anhydride. 
Propoxylated BisGMA was substituted for BisGMA in order to 
avoid any reaction of the anhydride with the pendant 
hydroxyl group in BisGMA. Monomer structures are shown in 
Figure 4.49. All samples, about 2mm thick, were cured 
between glass plates using 0.4 wt . % AIBN at 75°C for 12 
hours followed by a postcure at 160°C for 2 hours. 

Although dental composites are generally light cured in 
actual application, a heat cure was used to provide an ideal 
structure with maximum conversion. Maximum conversion is 
desired in order eliminate this as a variable in the 
analysis of property differences between anhydride and non 
anhydride samples and thus to prove the feasibility of this 
approach. Also, due to the differing reactivity ratios 
common in maleic anhydride-methacrylate copolymerizations 



147 



Propoxylated BisGMA 
/ =v CH 3 O 

CH, X / CH, N ' C 



Triethyleneglycol dimethacrylate 
o o 

CH 3 — CH -C -O — (CHj-CHj-O)^— C — CH -CH 3 
CHj CH2 

2-phenylethyl methacrylate Maleic anhydride 

CH 3 CH=CH 

CH 2 =C J \ 






C=0 O^ ">W ^O 

I 

o 
I 

CH 2 
I 
CH 2 



"\^ 



Figure 4.50 Chemical structures of methacrylate and 

anhydride monomers for dental applications 



148 



TABLE 4.8 Experimental matrix of dental monomer 
compositions . 

Sample ID Weight % in Monomer Mixture 

TEGDMA pBisGMA MA 

DM1 70 30 
DM2 70 20 10 
DM3 60 40 
DM4 60 30 10 
DM5 60 20 20 
DM6 50 40 10 
DM7 50 30 20 

(Bra89) , high conversions are desired in order to maximize 
anhydride incorporation. 

Polymerizations of 2-phenylethyl methacrylate (PEMA) 
with maleic anhydrides were used to model the dimethacrylate 
reaction. They were synthesized in bulk using 0.4 wt% AIBN 
at 75°C for 4 hours. The resulting product was dissolved in 
chloroform, precipitated in ether to remove unreacted 
monomer. The polymer was then filtered and dried under 
vacuum at 40°C overnight. 

We are using PEMA as a linear analog of the 
dimethacrylate BisGMA type monomers. PEMA copolymers with 
maleic anhydride should be linear and therefore soluble in 
common organic solvents. Therefore, we will be able to 
monitor the effect of anhydride incorporation on properties 



149 



such as molar mass and glass transition temperature which 
are more difficult to analyze in highly crosslinked samples. 
PEMA copolymer compositions are listed in Table 4.9. 

TABLE 4.9 PEMA-maleic anhydride monomer compositions. 

Sample ID Weight % in Monomer Mixture 

2-phenylethyl maleic anhydride 

methacrylate 

PEMA1 100 

PEMA2 90 10 

PEMA3 8 2 

PEMA4 7 30 

PEMA5 60 40 

4 . 3 . 2 .Copolymer Characterization 

Dimethacrylate dental resins . Equilibrium water 
content (EWC) was measured gravimetrically and the 
extraction of unreacted anhydride was monitored using UV 
spectroscopy of H 2 solutions from swelling experiments. 
Swollen, equilibrated samples were then dried under vacuum 
at 60°C to constant weight. Density measurements of the 
original dry samples and the post-hydrolysis dried samples 
were calculated using Archimedes' principle. These density 
changes along with changes in sample mass were used in order 
to calculate volume changes from hydrolysis. Details of the 



150 



experimental methods and subsequent calculations described 
above have been previously discussed in section 3.2.3. The 
results of this study are shown in Tables 4.10. and 4.11. 

TABLE 4.10 EWC of maleic anhydride dental resins. 

Sample Composition Equilibrium H 2 Content 

(TEGDMA/pBisGMA/MA) [%) 

70/30/0 4.12 
70/20/10 7.43 
60/40/0 3.81 
60/30/10 6.51 
60/20/20 11.53 
50/40/10 6.08 
50/30/20 10.94 

The dominant factor affecting the water uptake, shown 
in Table 4.10, is the anhydride content of the copolymer. 
Values vary from 4% for the two samples with no anhydride to 
11% for the two samples containing 20% anhydride. This 
result is expected considering the hygroscopic nature of the 
anhydride functionality and its susceptibility to hydrolysis 
to a diacid. An increase in TEGDMA relative to pBisGMA also 
seems to increase the EWC, but to a much lower extent than 
maleic anhydride. 

These swollen equilibrated samples were thoroughly 
dried back to a constant weight. Anhydride containing 



151 



samples showed a residual weight gain up to 1.55% as shown 
in Table 4.11. This weight gain is believed to be due to 
hydrolysis of the anhydride functionality. Multiple 
processes are occurring during the water uptake. Not only 
is the hydrolysis of the anhydride driving further water 
uptake, but unreacted maleic anhydride is being converted to 
maleic acid and then extracted from the sample. 

TABLE 4.11 Residual weight gain, anhydride incorporation 
and post polymerization expansion of maleic 
anhydride dental resins. 

Sample % Efficiency of Post 

Composition residual Anhydride polymerizati 
TEGDMA/pBisGMA/MA weight Incorporation* on % volume 





gain 




expansion** 


70/30/0 


0.00 





0.00 


70/20/10 


1.10 


0.94 


1.07 


60/40/0 


0.04 





0.00 


60/30/10 


1.11 


0.94 


1.08 


60/20/20 


-0.04 


0.84 


NA 


50/40/10 


1.53 


0.97 


1.67 


50/30/20 


1.55 


0.91 


2.11 



*Determined from the UV analysis of H 2 extraction solutions 
**Volume calculated from mass and density measurements 

UV spectroscopy was run on the swelling solutions. A 

calibration curve for the UV absorbance of maleic acid was 

determined in order to measure the maleic acid concentration 

in the extractables . All anhydride not extracted was 



152 



assumed to be incorporated. Incorporation efficiencies 
ranged from 0.84 to 0.97. 

Post polymerization volume expansions, measured using 
mass and density values, of up to 2% were calculated for 
anhydride containing samples. The expansion increases with 
increasing anhydride concentration. 

TG/DTA shows a significant difference in decomposition 
for anhydride containing polymers as seen in Figure 4.51. 
Initial weight loss occurs at a lower temperature than the 
pure methacrylate resins but the anhydride increases the 
thermal stability at higher temperatures. This is 
consistent with reported results of MMA-maleic anhydride 
copolymers (Bhu88). Increased thermal stability may be due 
to the anhydride unit blocking the 'unzipping' 
depolymerization reaction common in poly (methacrylates) . 

Linear poly (PEMA-co-MA) copolymer analogs . FTIR 
spectra were collected to verify the presence of anhydride 
in the structure. Figure 4.52 shows the comparison of the 
carbonyl region for poly (phenylethyl methacrylate) and a 
copolymer with 40 wt . % maleic anhydride in the feed. The 
absorption at 1727cm" 1 can be assigned to the C=0 stretch 
from the ester carbonyl in the methacrylate. The absorption 
of the carbonyl for the anhydride is present as a doublet at 
1781 and 1853cm -1 , for the asymmetric and symmetric C=0 
stretch . 



153 



^ 



o 



100 




i 1 r— 


1 




1 


1 1 1 1 






■"••^v 


l «s 


\ 




- 60/40 TEGDMA/pBisGMA 
-50/30/20 


80 










\ 

\ 


TEGDMA/pBisGMA/MA - 


60 












\ 

\ 


40 


- 










\ 
v \ 


20 


- 















- 


1 1 ! 


1 




1 


U 

.11,- 



100 150 200 250 300 350 400 450 500 550 600 

Temperature (°C) 



Figure 4.51 TG/DTA of anhydride modified dental resin, 



154 




O 
CO 

-Q 

i— 

O 

c/) 

-Q 

< 



poly(60PEMA-co-40MA) 



1728 




1800 1600 

Wavenumber (cm-i) 



Figure 4.52 FTIR spectra of poly(PEMA) and poly ( 60PEMA-CO- 
40maleic anhydride) . 



155 



The relative intensities of the 1726cm" 1 and 1781cm" 1 
carbonyl absorptions were used to calculate the ratio of 
PEMA to anhydride in the final copolymers. The final 
copolymer anhydride content, along with the measured glass 
transition temperatures, are shown in Table 4.12. The glass 
transition temperature of the PEMA copolymers increases with 
anhydride content from 43.8°C for neat poly (phenylethyl 
methacrylate) to 63.2°C for the 60/40 PEMA/MA copolymers. 
Actually, the anhydride content in the feed was 40 wt . % but 
the anhydride content in the copolymer is closer to 22%. 

TABLE 4.12 Glass transition temperatures and composition of 
PEMA-maleic anhydride copolymers. 

Polymer Tg* Anhydride 

(°C) content** 

(wt.%) 



Poly(PEMA) 43.8 



Poly (90PEMA-co-10MA) 47.8 



Poly (80PEMA-CO-20MA) 54.7 12 



Poly (70PEMA-CO-30MA) 57.9 14 



Poly(60PEMA-co-4 0MA) 63.2 22 



^Measured by DSC. 

** Calculated from the relative intensities of the 1726cm" 1 and 1781cm" 1 

carbonyl absorptions using the monomer mixture as a standard. 



156 



Efficiency of anhydride incorporation was significantly 
lower than in the dimethacrylate copolymerizations . The 
anhydride content in the PEMA copolymers is approximately 
50% of that in the feed. Because of the difference in 
reactivity ratios in maleic anhydride-methacrylate 
copolymerizations, high conversions are required to produce 
polymer high in anhydride content. Conversion, and 
therefore anhydride incorporation, in this system is 
expected to be lower than that in the dimethacrylate system 
due to the lower cure temperature and shorter cure time. 

The effect of anhydride feed concentration on the molar 
mass averages of the copolymers is illustrated in Table 
4.13. Increasing the anhydride content leads to a severe 
reduction in the average molar mass of the resulting 
copolymer. The Mn decreases from 63kg/mol for neat PEMA to 
26kg/mol for the copolymer with a 60/40 PEMA/MA feed ratio. 



157 



TABLE 4.13 Molar mass averages from GPC for PEMA-anhydride 
copolymers . 

Polymer Mn Mw PDI 

( kg/mol ) ( kg/mol ) 

Poly(PEMA) 62.9 245.5 3.9 



Poly (90PEMA-CO-10MA) 44.5 249.8 5.6 



Poly (80PEMA-CO-20MA) 30.5 192.7 6.3 



Poly(70PEMA-co-30MA) 36.0 169.3 4.7 



Poly(60PEMA-co-40MA) 25.9 122.2 4.9 



CHAPTER 5 
SUMMARY AND CONCLUSIONS 



The synthesis and characterization of amino acid 
terminated poly (acrylate) macromonomers using a cysteine 
chain transfer agent has been studied. The ability of these 
macromonomers to react with amide precursors in a 
condensation graft copolymerizations has been investigated. 
Although the novelty of this approach in terms of 
macromonomer synthesis, chain transfer chemistry, and 
condensation graft copolymerizations will be discussed, it 
is important to note the motivation for this study. 

Although at first glance the macromonomer and graft 
copolymer work does not seem to be closely related to our 
studies of dental resins, the motivations for these studies 
are tied closely together. The efforts of this research 
group have been focused on one main goal- increasing the 
understanding of the role of interfaces in composites and 
multiphase copolymer systems. 

The interfacial bonding between two phases is critical 
in determining the overall properties of composite (Arn97) . 
Much work has concentrated on surface modification in fiber 
and particulate reinforced composites (Arn97, Ore97) as well 
as compatibilizing agents in polymer-polymer composites with 



158 



159 



the goal of reducing interfacial tension and increasing 
interfacial bonding. 

One of the composite systems we have been investigating 
is the glass particulate reinforced poly (dimethacrylate) 
commonly used as dental restorative materials. The failure 
of these dental composites, and poor lifetime performance as 
compared to amalgam restorations, is generally attributed to 
a poor interface (Bra86). Although the glass-resin 
interface has been studied extensively, the source of 
failure is usually the interface between the composite 
restoration and the remaining tooth structure (Sod91) . 

Two of the main sources of this poor interface are as 
follows : 

1) the polymerization shrinkage during composite cure 
causing the restoration to pull away from the remaining 
tooth structure. This leads to marginal leakage, the 
infiltration of saliva and bacteria under the 
restoration, which can lead to the reincidence of 
caries . 

2) poor bonding between the exposed tooth structure, 
composed of hydrophilic proteinaceous dentin tubules, 
and the hydrophobic dimethacrylate composite. 

It is to this effect that a large extent of the research in 
dental composites has focused on one of two areas, the 
reduction or elimination of polymerization shrinkage or the 
evaluation of new dentin bonding agents. Only our study on 
offsetting polymerization shrinkage through the addition of 



160 



maleic anhydride deals specifically with one of these 
problems . 

However, the macromonomer and graft copolymer work was 
targeted to determine the ability to synthesize a copolymer 
capable of interacting with both the hydrophobic 
methacrylate and hydrophilic dentin structure at the tooth- 
restoration interface. Although the synthesized amide- 
acrylate graft copolymers were not tested in such a system 
and their aromatic structures may not make them suitable for 
this application, the feasibility of synthesizing the 
desired structures has been shown. The groundwork has been 
laid to synthesize acrylate graft copolymers with other 
amino acids more suitable to this particular application. 

Although preliminary work performed here (section 
4.2.3) on the possible applications of the synthesized graft 
copolymers was inconclusive, these graft copolymers may be 
useful in other interfacial applications such as 
compatibilizing agents in immiscible polymer blends, rubber 
modifiers, and surface modifiers. 



5.1. Chain Transfer Functionalization of Poly (acrylates) and 

Poly(methacrylates) 



Studies on macromonomer synthesis have concentrated on 
that of vinyl f unctionalized macromolecules . These 
macromonomers are thus capable of copolymerizing with other 
vinyl monomers in the synthesis of addition-addition graft 
copolymers. The novelty of the approach to macromonomer 



161 



synthesis applied herein lies in the ability to synthesize 
free radically polymerized addition poly (acrylates ) capable 
of participating in a condensation graft copolymerization 
with polyamides. It is the amino acid functionality which 
makes these macromonomers ideal for grafting or binding to 
polyamides or proteins. The conclusions for the chain 
transfer f unctionalization reactions are summarized below. 



5 . 1 . 1 .Conclusions for Preliminary Evaluation of Cysteine 
Chain Transfer Agent 



1) Under neutral pH conditions, the chain transfer 

f unctionalization of poly (butyl acrylate) using a 
cysteine chain transfer agent is ineffective. This 
reaction produces a polymer with a broad molar mass 
distribution, PDI= 4.8, and a higher than expected Mn. 

2) Chain transfer is inefficient due to consumption of 
cysteine in an undesired side reaction. Under neutral 
conditions, 5% of cysteine is ionized. The sulfur 
anion can react with butyl acrylate to form S- 
carbobutoxyethylcysteine . The consumption of cysteine 
by this side reaction leads to a decrease in effective 
cysteine concentration over time and therefore, reduced 
termination by chain transfer. 

3) The formation of the undesired side product can be 
virtually eliminated by reducing the pH of the 
reaction. A severe reduction in molar mass from 



162 



effective chain transfer is observed upon acidification 
of this reaction. 

5 . 1 . 2 . Conclusions for Synthesis and Characterization of 
Amino Acid-terminated Poly (butyl acrylate) 

1) The chain transfer polymerization of butyl acrylate in 
the presence of cysteine is highly effective. The 
calculated chain transfer constant, 1.49, is higher 
than that of other common chain transfer agents. 

2) The presence of an amino acid functionality from the 
cysteine end group is verified by a combination of FTIR 
spectroscopy, NMR, ICP, as well as by the ability of 
the macromonomer to react with amide precursors in a 
condensation polymerization. 

3) Predicted functionalities, using the Mayo model, are 
higher than those measured by the ICP-GPC technigue. 
This could be due to non-ideal conditions such as chain 
transfer to solvent, high conversions, etc.. and could 
also be affected by the inherent error in functionality 
determination using GPC molar mass values. 



5 . 1 . 3 . Conclusions for Synthesis and Characterization of 
Amino Acid-terminated Poly (MMA-co-QFPMA) 



Cysteine is not as effective, with a chain transfer 
constant of 0.26, in the chain transfer 
copolymerization of methyl methacrylate and 
octaf luoropentyl methacrylate. At equivalent levels of 



163 



cysteine, much higher molar masses are observed in this 
reaction than in the p(BA) polymerization. 

2) The difference between these two systems may be 
explained by the difference between acrylates and 
methacrylates . Other research groups (NAIR) have 
observed, although not to such a large extent, lower 
chain transfer constants for methacrylates. This has 
been attributed to the lower reactivity of 
methacrylates, leading to degradative chain transfer. 

3) The lower chain transfer constant and subsequent higher 
molar mass leads to lower predicted functionalities 
when compared to p(BA) macromonomers . Functionality 
could not be determined experimentally due to the high 
molar mass and consequent low end group concentration 
of the f luoropolymer . 



5.2. Graft Copolymerizations of Macromonomers with 

Polyamide Precursors 



There are few reports of well defined polyamide graft 
copolymers with addition polymers such as poly (acrylates) or 
poly (methacrylates) . Most studies of amide graft 
copolymerizations with addition polymers involve either the 
in situ formation of graft copolymers in polymer blends or 
radiation induced surface graft techniques. Although 
effective for their intended applications, neither method 
produces a well defined graft copolymer that can be isolated 
and studied. 



164 



The objective of this study was to synthesize such 
graft copolymers using amino acid terminated macromonomers 
synthesized previously. A summary of the conclusions for 
the graft copolymerization of these macromonomers is listed 
below. 



5 . 2 . 1 . Conclusions for Synthesis of Poly (amide-g-acrylate! 
Graft Copolymers 



1) P(BA) and p(FA) were polymerized with aromatic and 
aromatic-aliphatic amide precursors in a P(0Ph)3 
catalyzed polycondensation reaction. 

2) The products were extracted with THF and subsequent GPC 
analysis on extractables showed a bimodal distribution. 

3) GPC-UV results indicate that both components in the 
extractables contain aromatic segments from the 
polyamide. This would indicate that the THF soluble 
fraction is not composed of purely of unreacted or 
unfunctionalized poly (acrylates) , but contains either 
low molar mass graft copolymer or poly (acrylate) rich 
graft copolymer. 

4) Weight loss from extraction was much higher for p(FA) 
graft copolymers than for equivalent p(BA) 
compositions. This can be explained by an increase in 
unfunctionalized chains as predicted by the lower chain 
transfer constant in the macromonomer polymerization. 



165 



5 . 2 . 2 . Conclusions for Characterization of Poly (amide-g- 
acrylate) Graft Copolymers 



1) The presence of both amide and acrylate segments in the 
graft copolymer is verified by FTIR and NMR. 

2) Acrylate content was determined both by NMR and 
Elemental Analysis. Acrylate concentration in the 
copolymer is proportional to that in the feed and 
varied from 25 to 55 wt . % . 

3) For p(BA) graft copolymers, the concentration of p(BA) 
in the copolymer is 60-69% of the p(BA) in the feed. 
This is due to both the presence of unfunctionalized 
chains as well as the solubility of low molar mass, 
high p(BA) graft copolymer in the THF extraction. 

4) The incorporation efficiency for the p(FA) is much 
lower, 38%, due to the lower predicted functionality of 
these macromonomers . Steric effects from the higher 
molar mass of the macromonomer may also be limiting 
their incorporation into high molar mass graft 
copolymer . 

5) Inherent viscosities of graft copolymers are consistent 
with those of polyamides with molar mass values around 
15 to 35kg/mol (Hig80b) . The graft copolymer viscosity 
decreases with increasing p(BA) concentration. The 
effect is less dramatic for graft copolymers containing 
the higher molar mass f louroacrylate macromonomer. 



166 

5 . 2 . 3 .Conclusions for Mechanical Properties of Nylon 6/Graft 
Copolymer Blends 

1) Addition of PhDAA to Nylon 6 produces an increase in 
modulus and a severe decrease in ductility. The graft 
copolymer domains are behaving like hard inclusions 
within the nylon matrix. 

2) This behavior is due to the visibly poor mixing between 
the nylon and the PhDAA. Poor mixing is a result of 
the lack of thermal transitions for the amide phase on 
the graft copolymer not allowing flow during 
compression molding. 

3) Blending of the graft copolymer caused a decrease in 
all mechanical properties. Again mixing was extremely 
poor and domains were clearly visible. 

4) The graft copolymer had little effect as a surfactant 
in the Nylon 6/poly (butyl acrylate) blend. Again, lack 
of mixing would prevent the graft copolymers from 
migrating to the interface between the immiscible 
polymers . 



5.3. Offsetting Polymerization Shrinkage in 
Poly (dimethacrylate) Dental Resins 



Volumetric shrinkage is a major problem inhibiting the 
long term success of current dental restorative materials. 
This shrinkage is inherent to the free radical 
polymerization of the multifunctional methacrylate resins 
used in the dental composites. Polymerization shrinkage 



167 



creates both a weak interface between the tooth structure 
and the restoration as well as residual stresses within the 
composite structure, leading to premature failure in the 
restoration. Although various methods and different 
monomers have been studied to alleviate this problem, no 
solution to date has been discovered that eliminates 
shrinkage without significantly altering the cure and 
mechanical properties of the resin. 

The goal of this study was to demonstrate that we can 
offset the polymerization shrinkage of common dimethacrylate 
resins without significantly changing the comonomer 
structures through the addition of maleic anhydride. The 
conclusions for this work are summarized below. 



5. 3 . 1 .Conclusions for Characterization of Maleic Anhydride- 
containing Dental Resins 



Maleic Anhydride incorporation into heat cured dental 
resins was verified by FTIR, extraction, and UV 
spectroscopy. Efficiency of incorporation is between 
0.84 and 0.97. High levels of incorporation are due to 
high levels of conversion expected for high cure 
temperatures and long cure times. 
The equilibrium water content of the resins is 
proportional to the concentration of maleic anhydride, 
varying from 3 to 10% H 2 0. This can be explained by 
the hygroscopic nature of anhydride functionalities and 
resulting diacid functionalities. 



168 



Mass and density values of dry samples, before and 
after extraction, were measured in order to determine 
volume changes. Volume expansions of up to 2% were 
measured for anhydride-containing samples. 



5 . 3 . 2 .Conclusions for Synthesis and Characterization of 
Anhydride Copolymer with PEMA 



Maleic anhydride copolymers with 2-phenylethyl 
methacrylate (PEMA) were synthesized in order to 
determine the effect of the anhydride on properties 
more readily measured in non crosslinked polymers. 
Efficiency of anhydride incorporation was significantly 
lower than in the dimethacrylate copolymerizations, 
ranging from 0.45 to 0.60. Because of the difference in 
reactivity ratios in maleic anhydride-methacrylate 
copolymerizations, high conversions are required to 
produce polymer high in anhydride content. Conversion, 
and therefore anhydride incorporation, in this system 
is expected to be lower than that in the dimethacrylate 
system due to the lower cure temperature and shorter 
cure time. 

Increasing the anhydride content leads to a reduction 
in average molar mass yet a higher glass transition 
temperature in the resulting copolymer. 



CHAPTER 6 
FUTURE WORK 



6.1. Macromonomers and Graft Copolymers 

The overall results of this work indicate that graft 
copolymers of polyamides and poly (acrylates) can be 
successfully synthesized using cysteine end capped 
macromonomers. Although a series of macromonomers and graft 
copolymers was synthesized and characterized, optimization 
of the individual steps and extension of this work to other 
reaction systems should be investigated. Suggested further 
experiments are outlined below. 

6 . 1 . 1 .Macromonomer Work 

1) The effect of further reducing AIBN content on 
functionalization efficiency should be determined. As 
was stated previously, any chains initiated by AIBN 
will be unfunctionalized and reduction of AIBN 
concentration should yield more highly f unctionalized 
macromonomers. However, this is expected to be 
accompanied by a drop in overall conversion. 

2) The macromonomer synthesis could be extended to other 
monomers. For example, crosslinked systems may be 
investigated. It is expected that amino acid 



169 



170 



functionalized networks could be synthesized by the 
polymerization of dimethacrylates or any divinyl 
monomer in the presence of cysteine. 

6. 1.2. Graft Copolymers 

1) The reaction of acrylate macromonomers with a more 
processable polyamide would be of interest. Those 
studied here were soluble only in strong acids and 
showed no distinct thermal transition prior to 
degradation. 

2) A more soluble polyamide would allow for solution 
processing either for blending with other polymers or 
for more precise graft copolymer molar mass 
determination (GPC, light scattering) . 

3) More importantly, a polyamide that is thermally 
processable is of interest. Those synthesized in this 
study, similarly to other aromatic polyamides, degrade 
before they melt thereby complicating melt processing. 
Melt processability would allow for blending with other 
polymers and it would facilitate the sample preparation 
for the mechanical testing of the graft copolymers. 

4) It has been reported that, although these aromatic 
polyamides generally do not display a distinct melt 
prior to degradation, they are semicrystalline (Yos94) . 
X-ray diffraction on the synthesized graft copolymers 



171 



would be useful to determine their level of 
crystal Unity. 

5) If successful, the effect of macromonomer molar mass and 
content on the crystallization and mechanical properties 
of the graft copolymers would be of interest. 

6) The graft copolymerization of acrylates with naturally 
occurring amino acids such may be of interest in 
biological applications. Higashi (Hig80b) has already 
shown that poly (leucine) , poly (valine) , poly (alanine) 
and poly (phenylalanine) could be synthesized in the NMP 
solvent system used in this study. In fact, high molar 
mass poly (amino acids) up to 35kg/mol were synthesized. 
The polymerization with amino acids is where cysteine 
terminated polymers will be especially beneficial 
because of the built in stoichiometry of the amino acid 
functionality. 

7) Other methods of copolymerization of these macromonomers 
should be investigated. Interfacial polymerizations or 
bulk polymerization with caprolactam for nylon 6 
copolymers may be possible. 

6.2. Anhydride-containing Dental Resins 

Further studies in this research group on anhydride 
containing dental resins has been ongoing (Gra95, Wes97, 
Sch97, Meh97) . The work presented here represents the 
initial foundation for the ongoing studies. The effect of 



172 



anhydride incorporation on mechanical properties has been 
studied in detail (Gra95) . The incorporation and modeling 
(Wes97) of other anhydrides including nadic methyl anhydride 
(Meh97) and methacrylic anhydride (Sch97) has been 
investigated. 

The light or room temperature cure polymerizations of 
these copolymers has presented unique problems. 
Incorporation of anhydride is not extensive as compared to 
the heat cure systems (Gra95) . However several methods of 
improving the incorporation into dental resins- either 
through the addition of prepolymerized anhydride copolymer 
or through the addition of monomers more reactive with 
maleic anhydride, such as styrene or vinyl ethers- are 
currently under evaluation. 



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BIOGRAPHICAL SKETCH 

In keeping with his current sleeping schedule, Michael 
Perez Zamora was born at approximately 3:00 A.M. on February 
28, 1970, in Cincinnati, Ohio, to Pablo and Sylvia Zamora 
and to Bella Acosta, his grandmother. Approximately nine 
years earlier, Pablo and Sylvia emigrated from Cuba and met 
in Miami, Florida. They moved to Gainesville, Florida and 
married during the time Pablo earned his master's degree in 
chemical engineering at the University of Florida, almost 
thirty years ago. 

Michael lived in Cincinnati for three years before his 
father was transferred to Venezuela. After four years in 
Venezuela, and with Cuban Spanish speaking parents, he came 
back to Cincinnati a purely Latin kid who spoke little 
English. Michael adapted quickly to the American way of 
life upon exposure to Sesame Street, rollercoasters, theme 
parks, and baseball. Michael lived in Cincinnati until his 
family moved to Longmeadow, Massachusetts in 1984. During 
his time in high school, Michael was heavily involved in 
extracurricular activities including being named captain of 
the varsity swim and tennis teams. 

After graduating from high school in 1987, Michael 
enrolled at Georgetown University in Washington, D.C. It 



181 



182 



was during his time at Georgetown that he starting dating a 
longtime friend from high school days, the girl he would 
eventually marry, Karen Morey. After four years of having 
entirely too much fun, Michael went to work as an intern at 
DuPont, where he was first exposed to the real life 
implications of what he was learning at school. Michael 
graduated from Georgetown in the Fall of 1991 with a B.S. in 
chemistry and returned to DuPont for another internship of 
four months . 

After taking the summer off to sharpen up his golf game 
in preparation for graduate school, Michael began his 
graduate studies under the supervision of Dr. Anthony 
Brennan at the University of Florida in Gainesville in 
August 1992. Dr. Brennan, a professor of only one year at 
the time, quickly introduced Michael to the harsh and 
important realities of life. Michael settled in quickly 
with the help of Karen, whom he married at the end of his 
second year of graduate work. 

Life has come full circle for Michael. As he prepares 
to embark on his new career with Paxon, a division of Exxon 
Chemical Co. in Baton Rouge, Louisiana, he and Karen are 
leaving Gainesville almost exactly thirty years after his 
newly married parents, Pablo and Sylvia, left in their 
pursuit of the American dream. 



I certify that I have read this study and that in my 
opinion it conforms to acceptable standards of scholarly 
presentation and is fully adequate, in scope and quality, as 
a dissertation for the degree of Debtor of Philosophy. 



JA^didn. 




Anthony Jbt Br ennan, Chair 
Associate Professor of 

Materials Science and 

Engineering 



I certify that I have read this study and that in my 
opinion it conforms to acceptable standards of scholarly 
presentation and is fully adequate, in scope and quality, as 
a dissertation for the degree of Doctor of Philosophy, 




-7 



HM 



fames H. Adair 
'Associate Professor of 
Materials Science and 
Engineering 



I certify that I have read this study and that in my 
opinion it conforms to acceptable standards of scholarly 
presentation and is fully adequate, in scope and quality, as 
a dissertation for the degree of Doctor of Philosophy. 




Christopher D. Batich 
Professor of Materials 
Science and Engineering 



I certify that I have read this study and that in my 
opinion it conforms to acceptable standards of scholarly 
presentation and is fully adequate, in scope and quality, as 
a dissertation for the degree of Doctor of Philosophy. 




Eugene PV Goldberg 
Professor of Materials 
Science and Engineering 



I certify that I have read this study and that in my 
opinion it conforms to acceptable standards of scholarly 
presentation and is fully adequate, in scope and quality, as 
a dissertation for the degree of Doctor of Philosophy. 



fCiw^lki \j l^>i^ l 

Kenneth B. Wagener / 
Professor of Chemistry 



This dissertation was submitted to the Graduate Faculty 
of College of Engineering and to the Graduate School and was 
accepted as partial fulfillment of the^requirements for the 
degree of Doctor of Philosophy. 

December, 1997 




:red M. Phillips 
Dean, College of Engineering 



Karen A. Holbrook 
Dean, Graduate School 



LD 

1780 
1997 

.125 



UNIVERSITY OF FLORIDA 



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